Oh totally...I'm a huge Treasure fanboy, especially Treasure back in the Saturn and Genesis days. Gunstar Heroes is one of my favorite Genesis (or "Megadrive" if you're a weeaboo) games of all time that isn't Sonic.
Don't laugh, but Alien Soldier took me 2 years to beat. I first got it in early 2007 (at the climax of my obsession with oldschool games) and played it devotedly for weeks on end (when school wasn't eating up my time that is .) I even skipped homework to play more Alien Soldier. But ultimately I gave up when I doubted my ability to beat Epsilon 1 (the huge, purple metal eagle.)
Towards the end of last year I got back into it and played up to the point of 7th Force who, upon finding out it's a girl I threw my controller down and quit...I follow chivalry as a way of life so I hate fighting girls.
But early this year I managed to collect myself and beat 7th Force, and in the ensuing days I played to the end and beat Z-Leo (he's hard since you have to deflect his energy shots back at him.)
Exceeds Ocarina of Tim, which took me a year of constant playing to beat. Though I guess OoT took longer in the long run since I only gave up once (at the Water Temple) and it was only for a few months.
I too am a fan of treasure, and Alien Soldier just so happens to be my favorite side scroller of all time. It's a game I like so much, I am willing to pay large sums of money to own it (I haven't bought it yet but I will soon). Radiant Silvergun is another masterpiece, it's just too bad it was never released on any other console than the Saturn, which is why it's so expensive I guess. These kinds of games are simply timeless, 20 years from now you'll probably still see people playing them or buying them online.
What kinda tools did you use? I suck because I'm only familiar with Game Maker...that's about it. I am learning C/C++ as well as SDL though, so I hope I can fulfill my dream of making the perfect platform shooter.
Also, wanna see some of my sprites? The ones for the game I mean?