Play the game you most want to. I tried to 'finish' my backlog for two years when I realized that it had turned me off from gaming to the point where I hadn't played a game in two years! I would continue to try and slog through some dated game that was absolutely not fun to play, while continuing to buy new ones which were getting dated by the minute as well.
In the end, just play what you want to. If you've gotten a few hours out of a game, and there is a new game you'd rather play... accept this. Let go of the anxiety and accept that you won't get more hours out of certain games. Those that you bought new and sat around because you never got the time, bought compulsively, and can't stand playing through them... write them off as a loss.
Start afresh. It helped me fall in love with video games again.
Some games, just for the life of me just cannot finish - i.e. Darksiders 1 PC. No matter how much I like this game or really want to finish this game, it just ain't clicking, for whatever reason. Whether it's a tough boss or not sure of where to go next or what to do next - yeah, I dunno...
Some games, after a few hours - I've just had enough and am done with it...and don't even want to look at it or go back EVER. It'd like after a while, I feel like I've seen & played enough.
I was planning to go to something else like driving & racing games, after Xenus 2. I got the knack to play TDU2 for a bit and got back into that on Saturday - b/c of it's free-form and open-world nature. Got hooked on that for a bit - it's just one of those games I kick around and play, here and there. After having enough of that by yesterday evening, I tried to jump back to Driver: San Francisco - but dammit, one quest just drives me nuts (Lil Bay quest)...and I gave up on trying that quest, for now...
I played a (somewhat) older game of recently - i.e. Xenus 2: White Gold. And even despite its bugs; not-so-great text translation; having to mod the game up (throw in the Russian audio to fix audio issues and toss in Wesp's latest unofficial patch); having to reload older saves b/c of a glitch/bug/broken quest (and losing 5-10 hours in one part, and then again losing another 2 hours later somewhere else) -- I just couldn't put the damn game down. The gameplay, open-world, and questing was basically what I really wanted out of (the disappointing) Far Cry 2. There just was something about Xenus 2 - basically, it's a better-made and better put-together Boiling Point.
And dammit, now I got the same sickness w/ The Precursors - started that up last night after getting tired of Driver: SF's frustrations last night. I just intended take a quick look at Precursors and see how it is...and now I'm bloody freaking hooked. There's just something about these "shoot for the moon" and incorporate the kitchen-sink Russian-developed style of games like GSC's STALKER series and these Deep Shadows games that just seem to speak to me, even despite their technical issues, for some bloody reason...