I don"t see how skill systems are any harder to balance than a class system...you think WoW is balanced? hah.
UO was balanced because there was a skill cap...you just couldn"t be pro in everything. Sure you get alot of fotm, but who cares if it is fun? Make enough interesting skill tree"s, balance them with simple math that seems to elude most developers, and I believe you"ll get something far more fun than - hey look at me I"m affliction warlock #53453456346.
As far as rogues, I would say go look at DDO. It may not be what I consider a real MMO due to its MASSIVE instancing, but the action oriented gameplay coupled with pretty cool trap mechanics and platforming elements were really full of win. In fact, gameplay wise DDO was pretty damn fun IMO. Where it fails is using the D&D character system (which works well for P&P and single player games but not MMOs), overuse of instancing, and lack of a good pvp system.
On the topic of pvp, you know why I won"t try VG even though I"m bored of every current MMO? Yah, pvp...its either all or nothing, its not balanced, there are no objectives outside of straight killing, etc. Look, I enjoy interesting PVE encounters, but they are only fun the first time and it always gets old. Pvp is the spice, its basically free content for your subscribers if you set it up correctly the first time.
Please don"t make the mistake of adding on pvp at the last second. If you want to compete with WoW you absolutely need to incorporate pvp from the ground up. Objective oriented and balanced pvp...sure make it optional on some servers like WoW, but make sure its there. Just no retarded honor grinds please!