My impressions:
- While obviously a more minor point, the menus are pretty crappy. The announcer saying "okay!" every time you select something on the menu is immediately annoying, and the redone character portraits are frankly just crap. And while an even more miniscule point, it's a little odd that after you choose your character, the panel that slides down with your character's sprite on it doesn't make it all the way down before the game starts. Seems like a silly thing to whine about, but the reason I bring that up is because it contributes to the interface's generally unpolished feeling, particularly for those who have played Metal Slug 3 before.
- You can't set the number of credits available. This is dumb. The number of credits should changeable, but the achievements should be locked for anything above 5 credits. This provides incentive for players to challenge themselves, but doesn't require the rigor of a 1CC run. It's the best of both worlds.
- The frame rate seems to be too slow. I don't know if it's dropping frames or what, but the game just feels choppy. I tried comparing it with a couple of emulators and the JP PS2 version, and that only confirmed it for me.
- The slowdown is messed up. I'm not convinced that Metal Slug 3 has intentional slowdown, but even if it does, this release botches it. The slowdown is there, and it's even more dramatic than in the already slowdown-prone Neo Geo version. Bits where there's slowdown in the original also slow down here, but it drops even more frames and seems to last longer here. It's jarring when the slowdown ends and the game immediately snaps back to running normally. I understand that slowdown is difficult to emulate properly, but if you're going to have it in this release, give players the option of this faux-slowdown, or just playing the game without it.
- There's slight input lag. It's not dramatic, and certainly not as bad as the atrocious PS2 anthology's input lag, but it's definitely there. Try jumping in place in this version, and then in the MAME version. It's pretty evident, even though MAME, itself introduces some slight input lag.
- The scanlines option needs to be improved. The scanlines are way too thick. Players should have more options for scanline thickness, just like any emulator or the XRGB implements it.
- A number of sound effects are off. The sounds when the "GO!" arrow pops up and the bit at the end of a stage where the game counts up the POWs you saved are pretty clear examples.
Ultimately, I can't recommend the game as it currently stands. The various performance issues make the game play like a bit of a mess any time there's a lot of activity on-screen, particularly during boss fights. It feels imprecise, and if you're the sort of person who wants to get good at the game, the general sluggishness is a buzzkill.
When the emulated version of the game on the same platform is better and has been around for more than a decade, I have a really tough time telling someone that they should shell out for a flawed product.