The long-awaited list of cons of SWG is here. Just a few things I've thought up, and what others have mentioned.
A. Trial chat limit - 400 characters per 15 minutes. The workaround is using tells or groupchat, and the player senate is debating different solutions for the credit spammer problem soon, if they haven't already. Still is an issue for RPers, in it's current state.
B. Grindy combat missions - When you solo missions they tend to be boring, even though the combat system in itself is fast, fun and intense. It does get a lot more fun in groups, though, so find players of your level to adventure with. It is also very easy for a higher CL player to powerlevel you if they're in love with you or something and don't mind taking the time. Personally, I think you should go to space as soon as you figure out how to put a decent ship together, as space combat is a bit more fun solo, and gives decent ground xp if you're low CL.
C. Roleplay is hidden away - Not hard to get into, you just have to find it. Also quieter in the summer. Don't expect everyone with a RP tag to be IC and good RPers, there are just too many of them for that to be true. You can usually find RP in Outmian Yakta and the RP guilds, or set something up OOC on the RP chat channel. This is an important thing. Make a new chat tab and type "/chatr join chat.RP". The channel is where RPers meet OOC, aside from the forums.
D. There is a learning curve - With a lot of depth comes a lot of learning. Take your time and study things you want to try out, or just jump right into it, as long as you don't complain when things don't work out at once. It's not a Fisher Price toy like some people claimed after NGE. The ground combat system is also different from most MMO's, a lot faster, and the controls are different. Make sure to turn auto-aiming on in the options. PvE difficulty has been recently increased across the board, too, and even veteran players are finding it challenging again. Space is a different game alltogether, more akin to space flyers than any MMO's in terms of controls, but also sports the awe-inspiring depth of other aspects of SWG. I can answer questions ingame, on IRC, in this thread or via PM if you want, but the best way to get the whole picture is to read some guides on the forums.
E. Bugs - Yes, there are some in every MMO, and SWG isn't an exception. As always, the community exaggerates the relative amount of these bugs, but there are still a few quite pesky ones I've come across since my return, like getting stuck under terrain, being unable to trade for a while and someone's avatar displaying different clothing/armor than he was actually wearing. If you face a bug you can't work around, submit a ticket and the GM's will help you out very quickly.