The texturing and detailing looks incredible and the general map design is good, but unfortunately this is all hampered by how cramped it is. All the detailing makes you constantly get stuck or otherwise not move how you wanted to, which is very unfun and frustrating.
I enjoyed this map a good deal. Brooding atmospheres and dark, detailed spaces with engaging combat sucked me right in. Fun, not easy but not too difficult either. There's a great blend of exploration, run-n-gun, and set piece style fights; I'd recommend this to anyone.
So with many old classic WADs not aging so well or have their gameplay styles improved by modern WADs or even WADs that came only a few years later since their initial release, I begin wondering on how TeamTNT's other megawad, Icarus: Alien Vanguard, hold up today. Of course it's hard to not bring up TNT: Evilution when bringing up Icarus so I'll try to focus on Icarus in of itself for the most part. I played through with ZDoom 2.8.1 on Ultra-Violence with no freelook, jumping, crouching, etc.
First things first, the levels in Icarus are far more consistent than that of TNT: Evilution. As much as I like TNT: Eviltuon, the levels in Icarus carry a consistent theme with them (for the most part) and they all feel put together with a design flow in mind rather than a random compilation of levels. The worst levels of Icarus aren't as bad as they seem, and given that most levels are short and quick in action, you won't feel so dreaded on a level that seemingly drags on. There are some exceptions, some levels are longer and more difficult than others, and there's the occasional "where do I go" kind of level, but for the most part, you can play this WAD casually and enjoy it for what it offers.
Much like TNT: Evilution, Icarus experiments with some of its levels, MAP20 has one part of the level be an upside mirror or an earlier part of the level, only now you walk on the "ceilings" instead of the "floor", and MAP24 includes the ghost monsters bug as an intentional part of the map, there's even a small tutorial on the start of the map to tell you how to kill them, quite nice. My personal favorite levels are MAP11 and MAP22, but there are some other levels in Icarus that have a good variety of levels, both visually and gameplay-wise. Some textures do use the same textures over and over, especially silver textures early on, but they don't distract too much from the WAD, if anything it benefits some of the levels instead.
There's also a full complete soundtrack, with every level having their own unique track, compared to Evilution's smaller soundtrack that uses the same tracks for multiple levels. The music helps in making some of the worse levels more fun to slaughter though, MAP31 being my favorite out of the bunch, it builds quite an atmosphere for a level that I wouldn't expect to have any. All in the all, the music is great, but knowing TeamTNT, that is to be expected.
Regardless, Icarus is also pretty flawed, and some little annoyances can ruin a level. One of the notable examples like MAP20 have this lift that has a very tight space to stand on and very little room to straferun to the floor to enter that teleporter to leave the upside down area of the map. You can't stand on the lift for too long as then your head will supposedly hit the ceiling and the lift will go down again. It took me far long than it should to just get up that lift but because of how it worked, it ended up making an alright map to one I don't want to play without thinking about noclipping next time I play it. Some maps seem promising but end up not being so great or even frustrating to play. MAP18 didn't have much to offer other than a ton of Barons and Hell Knights in a big crate room with a Cyberdemon at the end (also a map-breaking error with the yellow key apparently). The two secret levels, MAP31 and MAP32, were pretty disappointing and were lacking compared to the main levels, with large spaces yet not so many enemies to nor much to look at.
The final map is the weakest map out of the bunch, but I guess that's expected. Anyways, the final map is your usual Icon of Sin boss level, and it doesn't seem so bad until you find out that you can just run all away to the other side of the map, shoot a switch, and shoot a target and kill the boss in less than 30 seconds. Not even any kind of lift like Doom 2's final map, you can stand where you are no problem as it is. It's strange how despite having three people making the map, it felt like it was made in five minutes by just one person.
Flaws aside, Icarus is still a good WAD to play and managed to age well (to me) despite some design choices that won't appeal to everyone. There are some bugs (like the one mentioned for MAP18) and some maps having inaccessible secrets (MAP15's shotgun secret), but for the most part, you can play Icarus problem free. Funny how I didn't liked Icarus initially and after this playthrough it became one of my favorite megawads to play through. Overall, Icarus is solid and still worth playing through.