This kinda reminds me of the Threewave "sillymaps", in a good way. Constant chaos & carnage. There's a few motifs repeated around the map that make for fun fights and movement: a mix of minor and not-so-minor levelchanges, the walls blocking LOS on a small scale, and the q3ctf1-like windows you can jump through. I've got no objections to the weapon placement. Bots also play the map fairly well.
I'll divide the rest of my comments between "things you could tweak while keeping the map basically the same", and "bigger changes".
*** Tweaks:
I'd probably recommend to juice up the accel pad arcs so they punt you all the way over the opposing pad. The situation to avoid is when a minor difference in jump arc, maybe just caused by the way you entered the pad or by stray MG fire, causes you to drop down a little early and get tangled up in thin rail brushes. And in any case, make sure the jumppad arc is bang through the YA; currently if you take off from the bottom lip of the accel pad it's quite possible to go under the YA without grabbing it.
Also clambering over the bridge rails to drop down to the RG feels fiddly. Maybe use a wider, more obvious & accessible drop-down spot? I assume you're trying to make it inconvenient to get the rail, but just putting it away from the action & requiring a drop-down does that. If you also introduce fiddly movement too, then once someone has to do that a lot of times it becomes annoying. Especially because the rest of the play on this map involves just bombing around at high speed.
That said, I'm not sure that sticking the RG down there actually does much to prevent this map from becoming a railer's paradise. You can drop down and get it quite easily & quickly. It could be more effective to put it out in the open, perhaps a new high spot in the center that you would have to climb or ride a platform up to while being exposed. The Quad could go down to the lava level, and the RA could go down to where the quad currently is, to break up the unusual armor trifecta in middle. (I haven't seen the earlier versions of the map, so I'm not sure how these comments match with other placement comments above.)
A minor note about the center area: you have 16x32 risers on the stairs. The "id standard" is more like 8x24, although other maps (including one of mine) have gone for chunkier risers anyway. You might want to try smaller risers to see if it feels smoother.
It's weird that the default jump arcs don't go anywhere for the circular jumppads. They're easy to use once you realize, but it's different behavior from almost all other Q3 maps. Note that the bots do use them OK currently, so if you fiddle with them check that bots continue to understand them.
You have "spawnflags 4" on the respawn entities; what's that for?
The 4 corner teleporters confused me at first. I'm a little dubious about the benefit of the "side teleport" flow, but assuming you keep it, maybe put an arrow decal on the floor by the TP entrance pointing toward the dest, for the benefit of dummies like me.
Bots seem to be able to handle the various paths & items, but they aren't interested in grabbing the MH -- or going up high in general -- or in getting the RG. That may just be the way things are, but if you want to try to tweak bot behavior, see
http://web.archive.org/web/200408110840 ... otopt.html
*** Bigger changes
First thing that jumps out is the huge open LOS down the center of the map. If the enemy team has human players who are good with rail, LG, or even MG, then any flag carrier is dead when they step into midmap. One partial solution would be to basically drop a huge block onto the current RA location, completely sealing off that center bridge. (Of course that messes up the RA/quad/rail item placements I was talking about before.) Might need a few other walls. Don't turn it into a real maze, but check where the really long & wide LOS are and ponder if there are simple solutions to block them.
(Another partial solution would be to ditch the RG, but I hesitate to suggest that because you don't want to REALLY anger the railwhores.)
The other major change I would find interesting has to do with the map's symmetry. Structurally it's mirror-symmetrical on two axes, which means that once you've seen one-fourth of the map you've seen the whole thing. Typically a map is more interesting if it's only symmetric on one axis, or if it's rotationally symmetric. This map looks like a candidate for rotational symmetry, or at least some minor bits of it.
For example, what if the accel pad to YA was only available on the "right-hand side" (as you leave the base). Or if the area around the flag allowed an attacker to come from a high/exposed vantage point on one side, and a low/shielded approach on the other. There's also some opportunity to make the teleporter arrangement more useful. The general idea is to give people reasons to choose route A versus route B other than just "where are the bad guys". Note that I don't think you need to turn a small/simple map into a large/complex map, but you can spice it up. There are a lot of different possibilities if you commit to breaking that symmetry.
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Any changes are ultimately up to you of course... you've certainly played & thought about this map more than I have. I do think it needs a bit more baking, even if you want to keep the same fundamental feel.
And just as an honest heads-up: if you're truly jonesing for high scores on LvL, a small funmap may disappoint you, because it will inevitably get dinged in the scoring.