Wow. Tough call between FNV and 2W2 for my suggestion. Both games offer a lot of fun gaming time. FNV offers some really good companions who are more believable than most. The writing is top notch though I found the environments in the game to be mostly mediocre. I found Fallout 3 a much more fun world, but FNV felt much more alive as far as people go.
Two World Two is fun mostly for the exploration and all the crazy crafting you can do within the game. I found the love interest in the game to be well done and several of the quests are just a heckuva lot of fun. The weakness of two worlds is probably combat, but if you respec and keep swapping between melee, archery, and magic, it never gets too dull. I found the most fun out of being a mage, but that's my proclivity anyway. The horse racing quests were dull, but skippable. The endgame story is lame, but getting there is pretty entertaining. I didn't think much of the pirate add-on but it wasn't terrible either.