I was in the 40s when I got to Alduin, with a daedric bow and archery skill in the 80s or 90s. Don't think I particularly struggled with him.
Games I've abandoned...AssCreedBro. I got to the part where you save the Countess or whatever, then simply never played it again. No idea why, just lost interest. Haven't picked up Revelations either.
Ninja Gaiden (2 maybe? The one with the blonde with the physically impossible breasts) on the 360 I also gave up on. There was a winged demon boss in a cathdral of some sort that was unbeatable. I tried, tried and tried (even getting the achievement for dying 100 or 1000 times or something) and couldn't do it. Left it frustrated and maybe 18-24 months later, had another go and beat him on the 2nd try. Went on to finish the game after. Was a silly, very hard if enjoyable game (in a masochistic sort of way) that I can't see myself ever replaying. Yahtzee's review was enough to convince me 3 isn't worth bothering with.
Lastly and most recently TW2. It was before they released the Enhanced Edition that radically changed the combat and the start. I keep meaning to try it again.
I don't know if it counts the same as a first time playing a game, but I have left subsequent playthrus in the middle after finishing it previously at least once. Think I currently have a DE:HR save in China, Skyrim just after the start (not even at Riverwood), NWN2 just after first silver shard, Mass Effect (thought I'd do a run thru 1&2 before 3 with all the choices I wanted) but 3 came out before I finished 1 and also FNV. I broke the Honest Hearts DLC so couldn't even start it properly because of stupid game design, couldn't be bothered with the rest.