Okay OP, I will give you my honest answers, as I have recently returned and have been back for about three weeks. However--- I do not know what the game was really like at the time that you left, as you sound like a relatively newer UO player than I was. I returned from a departure since sometime in 2001 or perhaps close to 2002. At any rate we were well into Tram & Fel and we still used Felucca moonstones in those days.
So my impressions may differ from yours as far as what I missed and what is new/different since I've been back.
I, like you, left UO-- not FOR wow, but just because it seemed like the game I liked playing was gone. A year or so into the 2nd Age, I couldn't say the game was really deserted--- but it felt that way. There had been a turnover and the crowd had changed. People who weren't present in UO's first two years really would have a hard time knowing exactly what I mean by this-- but we really had Community. I don't mean we just sort of had a good pep spirit about UO, I mean that, literally, we had Community. Like you knew most of the people who frequented whatever town was your "home." Most people didn't own houses. Most people wound up being guildmates, party members, friends or hunting partners with the people they bumped into at the bank all the time. You went to the weapon/armor shop in town and nearly always, there was a player there working on smelting or blacksmithing, who would repair gear for you. (No repair deeds.) People had a sense of pride in where they were from. The game was full of its problems too (like a virtual mafia always buying out all the reagent respawns and reselling them on vendors at inflated rates) but it had flavor. The first and only home I owned back then was the tiniest possible two story sandstone (the 2nd floor was really nothing but a roof with enough room for a loom and a small table or something) which I co-owned with another person because home space was so scarce. There were always enough people wandering through (either exploring or taking travel shortcuts) the wilderness that no matter where your house was placed, you could make some money off NPC vendors at your house, without even going much out of your way to advertise it.
I think at the time I left, that flavor was gone. Much more had been done, in part because of what I would call the "casual demand", to solo player-ize the game. First off, nearly everyone had all their own professional mules and thus no one needed to cross-trade services between accounts anymore. This was in part due to the addition of more character slots which goes way back, but still, had an impact. It's no fun to be making your blacksmith and realize that absolutely nothing you can make will sell to anyone because everyone else already has their own GM Blacksmith alt. That's black mark one which starts a community downhill, IMHO. In order to help players "catch up" and/or level up alts quickly, they also introduced power hour and other changes which (I am not sure if they are still present per se) did things like assign "most effective hour" per day for you to spend on your char for skill gains. I'm not sure if the player base changed first, or the patch changes affected the player base, or what. But I think community was lost in this era and more of a power gamer mindset took over. Everyone always wanted to be 7xGM... but I think in the past, it took people months, years to do it. This era felt more like a large number of players just signing on for an hour to do thier power hour, and not really playing the game until after they got their 7xGM... at which point all they did was PvP or farm. It seemed that way to me, anyhow. I lost touch with most of my old crowd and freinds, I believe most stopped playing and bled off to EQ or other games. But really, none of us had been actively playing daily for a long time by the point at which I left.
I didn't leave "for" anything, I only picked up WOW (which I sorta always had the suspicion deep down was a cheap, cheesy powergamer template game and of course is by Blizzard which is like the Taco Bell of gaming - popular but no substance) because a friend literally shoved the free trial CD's on me maybe two years after I left UO. I'd kinda sworn off MMO's-- almost worked.
Yes, everything about WOW left me nostalgic for UO. WOW hardly bothers even attempting to make any sort of community.... anything you need you can alt, or auctionhouse. No need to deal with other bothersome players, at least until you get into max level raiding and dungeons for farming high level gear. And as was stated earlier in the thread, the WHOLE GAME is about itemization and gear, and you are always pouring hours into trying to farm or earn the next best piece, only to have it made obsolete in the very next patch or when the next tier of gear is released. And this pace entirely caters to the 1% or so of the playerbase that plays obsessively hardcore, conquers all the new dungeons in the first two weeks after a patch, that sort of thing. So most of the rest of us straggle along afterwards unable to get into the best guilds, top end raid dungeons, or daring to PvP because we're woefully undergeared at any given time. Kind of a pathetic design IMHO catering, despite the marketing ploy of being the "casual MMORPG", very clearly caters to people who make real life secondary and adjusts new content and releases at their pace, rather than the majority's.
As far as since I've been back... the game is still deserted. You can wander around for hours and not see anyone. PvP is a total joke-- the same hacked up people corpsecamping their inferiors and fleeing from their equals. Don't even bother going to Fel, pretty much. There is nothing there except ganking and griefing at Fel Yew and that's "PvP." If you want real PvP you're better off joining a guild and doing duels with your guildmates and such-- at least then you won't be repeatedly griefed, which is all but assured in Felucca. If you aren't in a guild, the world is going to feel pretty empty. Going to Luna does not exactly fill me with awe about how many players are still in the game--- the fact that most of the people present in Luna at any given time are completely idle, unresponsive, and you will see them still standing there in the same position if you recall back to Luna six hours later, doesn't help. So, if you do come back, join a guild. It is pretty much the only way you are likely to run into more than 1-2 people per hour. There are still players out there actively playing, but they're recalling around from house to farming spot or from farming spot to bank and you're just not likely to see them or run into them at random. (A side rant would be that I think the prevalence of recalling also helped turn the game into more of a farm fest.... if I could take over as dev, one of the first things I'd do is put a fifteen minute cooldown on any form of recalling or gate travelling. It would be amazing to see how much the old cities would be revitalized if in between treasure hauls people either had to stand around and talk and do things in town, or travel overland by horse or foot.
(This is more how things were in the very oldest days.... when half the players didn't even know how to recall and didn't have magery anyhow, and there were no runebooks.) But, if you left and tried WOW and really found it lacking next to UO, then as others have said, there really is nothing out there that is going to give you the UO character. Even if UO is a shell of its former self in a lot of ways, and has emulated the template MMO's in a lot of ways (like the gear and progressive stat/skill cap increases over time, which encourage and cater to powergaming and ideal template building and farming rather than RPG'ing. It really is true that all the rest out there are the same, mass-saturation addiction template forcing you to level, grind, and delaying gratification on giving you temporarily great rewards which are constantly made obsolete soon after you get them.
I guess: don't come back because you believe UO has undergone a Renaissance or has been repopulated. It hasn't really. Come back if you know you liked the things in UO that no other MMO offered.
