Since I'm usually able to eventually beat all the games I start playing (without cheating), this is a hard one for me. Don't get me wrong-- there are still plenty of games I have left to finish that I've started, but I have game plans with nearly all of them.
I play games perhaps in a different way than many others-- I play long sessions, with short spurts of different games throughout. I have some form of ADHD so I generally can't play the same game for long hours on end. The exception is with RPGs, sometimes I will spend a couple hours at a time on these just because of the nature of the game. For me, a good gaming session is where I make a little progress in a lot of games. For non-RPG games I find it incredibly difficult to sit myself down with a single game and play the shit out of it until it's done, or even to focus on a single game for days on end until it's conquered. I lose focus after a while and have to play something else. Because of this, I have many games in progress that I've been working on for quite some time, but it's not because I'm stumped by them or anything as I have full confidence I'll be able to complete nearly 100% of them in time.
Having said all that, there is one Turbo game that has me truly befuddled, and I'm not so confident I will ever complete it. That game is R-Type. I can make it as far as Stage 6 on a good day, Stage 5 on a bad day and that's after owning and playing the game for a decade, plus. Those later levels require such pixel-perfect timing and memorization, you (as a player) are forced to play the same portions over, and over, and over again until the right path and actions are forever ingrained into your head. Because of my mild ADHD issues, this kind of game play isn't a recipe for success. After just a couple continues I usually have to turn the game off and play something else since I lose interest quickly. When that disinterest sets in during a gaming session, my game playing ability goes to shit as my mind wanders and my focus dissolves into thin air. Although I'm much better at keeping focus on things in general now compared to when I was a kid, I learned a long time ago the only real way to regain that focus while playing is to play something else.
Anyone who reads my postings here knows how much I love a challenging shooter, and in the end, I can usually best whatever you throw at me given some time (or quicker, even). I fear that in this case Irem may have actually pulled off what was previously thought impossible-- they have effectively "stuck it to me."