The classic client is the reason why UO's playerbase will never grow again.
Actually, the classic client is the least of the reasons why the playerbase is stagnating... The correct reasons are:
1) The new client attempts to divert itself over to the MMO standard without taking into account the fact that the MMO standard game is an entirely different game. UO is a diversion from that standard. The MMO standard is a leveler with a limited amount of customization; while item properties may be on the verge of ridiculous, you also have a very finite amount of those items you can carry. The fact that each bag in the SA client can hold 125 items, and that the default view is the MMO standard grid view is actually a detriment to the new client because it is difficult to manage -- in addition, in MMO standard games, when you hover over something, you get full item details, while in UO you get the item's name and must then click to get full item details. Thus, rather than taking the appropriate route of teaching someone to use a freeform backpack during a tutorial (see next point), you end up with what can be a very confusing interface.
2) The tutorial for UO teaches you some things, but glosses over others. You should leave the new player tutorial knowing just about everything there is to know about the game, from how your skills work to how item properties work to how resistances work, and where to click for what based on whatever custom modes your client is in. It currently does not, and because UO's new client is a mish-mosh of UO-standard and MMO-standard interface components (heck, there's not even any consistency on what right-clicking a gump does -- sometimes it cancels, sometimes it doesn't).
3) The quest systems are another major problem in that whenever the quest system is updated, any quests relying on an older quest system should also be updated to that new system. Currently, there are, I believe, three different quest systems in play. One is "The Naturalist," the second I forget, and the third is the UO:ML style. Additionally, while I understand the reason for needing to flag items as quest items, the flagging of items causes issues if you're on different quests using the same items. In other games, this is a non-issue.
All in all, there are aspects of this game that just don't match the MMO standard (though, I'd pay for a 2D client right now that had modal chat), but there's little to address that difference.
What I will say is the Enhanced Client is a far cry closer to the UO:2D client... but in retrospect, from a graphic standpoint, it's a shame that the 3D client got waxed, because at least in the 3D client, your characters and mobs were 3D graphics, not 2D animations.
There are also technical issues with the Enhanced Client that the Dev Team simply do not understand. They are evidenced by statements like they had to re-render the mobs at a lower quality because the game wasn't able to handle the textures and was causing lag -- sprites don't have textures. They are also evidenced by the fact that I can run around Dalaran in World of Warcraft, which has textures and items and hundreds of people and particle effects out the wazoo and only notice my system hiccup a little if I hit a VERY crowded area... otherwise it's smooth sailing, and yet, in UO, where there is no sky to render, and the only textures are the ground, because the walls and objects are also 2D pixel objects, prior to the revert to lower quality graphics, I was stuttering and stumbling in Enhanced (and trust me, it's not my system doing it...).
All of this said, yeah, the graphics of SA are less ... resolution than KR (I will not say less quality, because the KR graphics were hideous), but the Dev Team is taking the proper approach to the client and ensuring stability before bells and whistles. Hopefully they will get the Enhanced framework solid, and then be able to build from there. Personally, I'm very close to making the switch to Enhanced... I just need them to fix the cursor sensitivity in the legacy container mode (because I am not playing with 125 grid tiles, nor is list-mode convenient), and perhaps be nice and put in a journal-save option like 2D has. Other than those two things, Enhanced can, at very least, do everything that the 2D client can do, and in some places, it does it better (remember, there's no atlas in the 2D client).
Thanks! 
