Due to a few oversights, the PC port of this game teeters on unacceptable.
I'd precaution that I don't think this game is a bad game, I just can't recommend this version.
I bought this game in a sale a while ago and am just playing it seriously now. If you have any interest in this game, and if you own any Nintendo handheld from the DSi onward, buy that version instead. I haven't played the DSiware version, mind you, but from videos of gameplay I figured the PC version would be somehow better in it least resolution, but a better look at the graphics here only serve to the games' detriment; the native resolution on the DS makes it look as if it were a unique step beyond 8-bit, the 2 options (windowed and fullscreen) on PC make it look like poor mockery of a NES game. One problem I have which I presume is present in both versions is that the sound design (other than the music) is inconsistent with the "retro" theme, with some sounds being appropriate and some just being poorly masked modern sound effects, which is jarring when noticed. I had to drag the windowed screen to a much smaller size to make the graphics decent looking, and also put the sound effects down to minimum and the music 3 notches above it - there was some definite oversight with whoever made the default options so bad. If you've made the same mistake of already buying this version of the game, this is at least the most optimal way to play it.
Now, my biggest gripe with this port is the blatant removal of an integral feature: the map. The DSiware version gives it to you on the bigger top screen the entire time, like the DS Castlevania games. Here, Mr. Tesla is constantly referring to having updated your map, and THERE IS NO MAP. There isn't even a button to bring it up. You could argue that the map is unnecessary given how simple the map is, and maybe this is a direct throwback to Metroid I & II, but again, it is CONSTANTLY referred to in game, and those are the only games in the series that are too obtuse to play now without the use of a guide. I could have overlooked it here if they only removed that from the dialogue. That Capcom hasn't is obscenely lazy, and as a result, there is no justification for having released this game in the state it is in.
I had no issues with the CD-Key, but it was still an unnecessary and inconvenient step in the process further defining this version as the inferior port.
Edit: Nevermind, the M key brings up the map, which is explained nowhere and I had to find out online! Bumped up the review score to reflect this.
Now that I've given the game a fair shake (and vice-versa) I'm more able to critique the finer points of Dark Void Zero. First off, the story is batshit crazy science fiction (the good kind) right out of the gate. Unlike Dark Void proper, there is no dwelling on boring earth stuff and whatever Nathan Drake was up to before World War II broke out. Here you play as Rusty, who was born inside the Dark Void itself, to a couple within a group of survivors trying to stop the Keepers from taking over earth while stranded in their dimension with good ol' Tesla. It is truly a shame that this wasn't the console game's story, as it would've been much more compelling from the beginning if this was the sort of thing explored in fully rendered cutscenes.
I would hesitate to call this game a Metroidvania, as the odd approach to the formula here not only fails to fall into those conventions, but falls short of them as well. You get checkpoints in this game, but not saves. Not even passwords like Metroid had. The game's short length is its excuse on this front, and may have been sufficient had it just been a forgotten DSiWare title, but presented as a Capcom published game on Steam with no mention of the DSiWare version, it isn't enough when compared to all the similarly styled games on the same market that do more with much less money.
Not even its pretend origins as an unearthed "8-bit classic" that never saw the light of the day justify this. Sure, there are plenty of NES games without passwords or save systems, but of all the ones I've seen, I can't think of a single one with a focus on exploration and backtracking. Not only that, none of those games were technically advanced enough to have maps - it was Super Metroid in 1992 that kicked off this trend. This, and my aforementioned issue with the sound effects, make this game painstakingly anachronistic. I shouldn't be asked to play this type of game in one playthrough, regardless of difficulty or length.
Side Note: a game shouldn't be allowed to falsely claim it was some "legendary project" that was scrapped decades ago, especially when its actually published by Capcom and there is absolutely no indication that it isn't. I've just now in 2016 discovered that there is no way this can possibly true, after just accepting it as such since both games were released in 2010. I thought that was really cool, and its probably why I was interested enough to eventually buy both games. I'd have more respect for such a move if they had conspired to make this a company wide lie and applied it to the original Dark Void, where none would be the wiser until some ex-Capcom employee exposed the lie and it became a scandal. It stands as simple deception, and just kind of sad, regardless of intentions.