Aperture Tag: Introducing a wonderful game mechanic
The backstory here seems to be set at some indeterminate time (presumably between the two games). You've been awoken from stasis by 'Nigel', who is going to test your use of the paint gun. The story is pretty ok, given that this is a mod. It does a good enough job of setting things up. However, personally, I don't think the story is too important here.
The concept of the paint gun is well thought out, based on one of the original concepts behind the portal 2 game. As far as its implementation, the paint doesn't actually come out of the gun, but just in front of it. A minor note, as once you get used to using it you stop looking at the paint coming out anyway.
I'm still not entirely sure I get the right concept behind the "paint enabling/disabling" fizzlers, but through trial and error I figured it out well enough to play properly.
The levels are well designed, offering a good range of puzzles. There is a very nice mix of old, modern and 'outside' style puzzles. A minor annoyance is the extended time it takes to travel between some of the test chambers through long pipes. The developers probably could have cut that out and not lost any value.
I played using the keyboard/mouse. It looks like it supports controllers, but it is first person, so I wouldn't bother trying a controller.
The graphics are mostly good. The new assets look very nice in this mod. The gun looks very nice. However, for some reason when I play assets involving 'glass' do not seem to render correctly all the time. Occasionally switching between tinted and fully transparent. This doesn't really give much cause for concern though.
The soundtrack to this is great. Partly done by Harry Callaghan, it captures the style of portal really well, while avoiding being too samey. Voice acting for Nigel was good too.
I completed the game in about 4 hours, so it's fairly short, but there are a lot of community-made maps, and a level creator, similar to the original portal 2 game, so there's a lot more levels to try after completion.
I found no game-breaking bugs in this mod, and there were only a few minor annoyances [like the glass rendering bug], and something seemed a bit off when I was modifying the key bindings in the menu, but that didn't affect gameplay.
This mod is great, and any fan of portal should definitely try it. The paint gun is a great addition. My only request with the mod is it could have done with a lot more of the fast-running parkour style levels.