I thought I'd talk about Risen3D, which I've been using for years.
plums already mentioned some of the cool aspects of Risen3D, including its very smooth feel. I just played a bit of BTSX Map01 on GLBoom and Risen3D. As a keyboarder who does all his movement on the numeric keypad, the feel of Risen3D is far superior. There is really no comparison in the smoothness.
I agree with plums that the high-rez textures look awful, and the 3D models look like they're walking around with a stick up their ass. Thankfully, they are not activated by default, you have to deliberately download and install them. My advice, don't. ;)
Risen3D is a GL-only port, which is fine by me because I'm a GL-only player. GLBoom looks pretty decent, but Risen3D definitely looks a bit better to my eyes, and better than GZDoom as well. Default gamma is just the way I like it on Risen3D, which sees well in the dark but isn't over-bright. Another advantage over GLBoom is that the Mordeth bridge in BTSX Map01 looks perfect, but in GLBoom you get a sky texture under the bridge instead of the nukage.
Recent versions of Risen3D have added splash effects and glowing objects, and these appear to be on by default if you launch R3D with ZDL 3.2, but if you use the R3D Launcher, make sure you go into Advanced Options/Sounds and turn off 3D Sound, since this is the only way -- and very unintuitive at that -- to get rid of the horrendous custom sounds that are on by default. Launching Risen3D in ZDL 3.2 seems to get around this problem.
Movement in Risen3D with Always Run enabled is not only smooth but seems to be slightly faster than in other ports. Some jumps that seem to just barely require strafe-jumping in other ports can be accomplished running straight-ahead in Risen3D.
For those like me who hate infinite-tallness, it is turned off by default in Risen3D, and I can't see a way to turn it back on. Yay. Risen3D also supports mouselook.
Risen3D is supposed to be fully Boom-compatible, but during the Mayhem2048 DWMC thread, R3D failed to properly run Map16. I've also noticed Boom-fails, such as a Manc, struck by a Cyb rocket, not quite being knocked off a platform but instead sinking into it and becoming helplessly stuck on Map25. A Lost Soul also became stuck against a wall.
I've experienced other irritations with Risen3D, such as being unable to figure out how to add custom elements, such as cc4-tex.wad, in the R3D Launcher, and instead having to laboriously add the texture pack to the folder R3D creates containing the WAD file, and then it appears in the launcher window. Where's the file browser?
Risen3D also seems to lack a monster/secret counter, unless i missed it somehow.
Also on the list of negatives is Risen3D's touchy auto-aim, which aggressively targets the closest monster, even if it's a mile below you. This makes shooting rockets across gaps very dangerous for the player if unseen monsters lurk below. In this regard, R3D seems as bad as Doom.exe. Yet another issue is that it seems R3D is not the best port for Zerk punching. I've suffered far more damage, and been forced to land many more punches, against Pinkies in R3D vs. GZDoom.
One of the most memorably annoying examples of R3D's overl-aggressive auto-aim occurred on E3M8 of cannonball's Concerned. Near the end, you have to stand on a platform and shoot rockets into a small opening in a wall, to start a reaction that pushes a Sergeant across a teleport line and does some business with a Spider Mastermind or something. The Sergeant is located behind the wall at floor height, while the small opening you shoot through is close to 128 above the floor. When I played, R3D relentlessly kept targeting the Sergeant, and as a result, it was impossible to complete the level, a real bummer since it's long and very tough. I surrendered a lot of pelts even on HNTR, and had to DNF the map. This issue did not occur in GZDoom.
Irritations like these are a primary reason that GZDoom is becoming my port of choice. In spite of this, I still love Risen3D for its many areas of superiority, especially that all-important feel. One thing I hope to accomplish this month is a nice email to Abbs mentioning all these issues. I might copy/paste my post. ;)