Oblivion and Skyrim are both awesome, if you like games who focus mostly on exploration and don't mind filing the gaps with your imagination. However, if you plan on playing both, I'd suggest starting with Oblivion. If you start with Skyrim, the other one might seem "old" and lacking of some functionnality.
If you're going to buy an elder scrolls game, check out oblivion and then skyrim. Morrowind was great but now it will feel dated and some things are a pain in the ass that were made much better in the sequels (alchemy for example.)
Also check out Age of Wonders III.
I've been reading that there is a big community of people who have modded Morrowind to keep it up to date graphically as well as improving the UI and such. Has anyone tried any of these out?
Wow, just checked out Age of Wonders III. That looks awesome. RPG strategy hybrid!
Get some Sup Com FA on that list and some UT2k4/UTC and you'll have yourself one hell of a list.
Planetary Annihilation?
These look good as well. Sup Com FA isn't too expensive either so I'll probably try that before PA I think.
I'd like to add Assassin's creed II to OP's list. The recreation of Rennaissance's Italy is truly wonderful, and the missions are quite cool too.
I have AC:Brotherhood on my wishlist atm, I guess that's the one after II? I'll add II as well because I do want to play a game based in that era.
Watch Dogs (Best Game of May)
Did you check out watchdogs?
I'll probably wait a while for this one to come down it price. No rush for me, I have tons of games to get through first.