Nexzr is incredible, it's one of my favorite shmups of the generation! It's definitely in my top 5 for the Turbo/PCE, which puts it high on an overall list since I do think that console is the overall best ever for shmups. It's a fantastic classic shmup with some of the best graphics, music, and gameplay around. It's hard, but with practice, thanks to its infinite continues it's definitely beatable. It's a bit like Image Fight, which is a fantastic game...
As for what separates the original version from the Summer Carnival version other than a whole bunch of money, though: the Summer Carnival version removes all of the cutscenes from the game, but adds the carnival mode with its new exclusive stage. Additionally, the new cover is just plain white, instead of a nice shot of the ship and such, so many people will surely prefer the original cover. The only other change I know of is that Naxat Soft added saving to the game, but unfortunately ONLY for carnival mode -- the game will save your best scores in carnival mode to a save file on the console, but will not save your high scores for the main game. Additionally, if you beat Nexzr you unlock a level select in the options menu... but since it doesn't save anything, it's not too useful. Unfortunately I believe that the Summer Carnival version works the same in that regard; the save file is, again, only for the new, carnival mode part of the game.
I bought the Summer Carnival version of the game for two reasons: it's a lot cheaper, first, and I don't like the story so having a version without the two cutscenes of the original game actually is kind of a positive. Watch the cutscenes on Youtube if you want, though; they do have good music, so that I miss from the Special version... oh well. The two cutscenes are one that goes at the beginning before the first level, and one before the last level (final boss). The ending, which is pretty much just a credits sequence, is left intact, if I recall correctly, since there never was plot there.
