As someone primarily interested in singleplayer experiences, is the unreal bundle sale of any interest to me? I have never played anything like it, having been a console only guy until 18 months ago, and I am intimidated by the knowledge that the multiplayer parts are only really played by highly skilled players, it would be pointless me even bothering.
Unreal is still one of my favorite single player FPS games, though it's hard to say how much impact it'll have today. At the time ... well, I can't even put into words how amazing it was. And compared to modern shooters, it is LONG.
Unreal 2 is a much lesser game. Most of the UT games have pretty good bot support, which is actually how I like to play them if I need a quick fix. In fact, playing a lot of UT with bots might be a great way for you to warm up to playing real Multiplayer.
And of course, if you DO want to jump into MP, UT is unsurpassed. I even love UT3. Great bundle really.
Edit: In fact, typing this out has tempted me into making tonight an evening of all things Unreal. Been a while.