It's not going to result in ridiculously high frag counts, but you won't get bored playing it either. There is no ugly on this level, but there are a few areas that could have used some improvement. First of all, there are no cogs. Now, as far as I'm concerned, this level is proof that a level can avoid cogs completely and still be a blast to play. A level doesn't need cogs to be good, but having them almost always improves the level.
Size is the other issue at hand, though a more easily debated one.
In my view, this level might be a bit too big, and could have stood to lop off a few areas. Of course, most of my games are of the four player variety, and I like a fast paced deathmatch. For many of you, bigger is better, and if the size isn't an issue to you, there's not much left to hold against Complex 1. This level has been out a while, and already has a good fan base. If you haven't tried it, I suggest you do so.