Under becomes a boring drag so often because it is very difficult to destroy the bases. This can be solved by either removing all base defenses and leaving a redundant Power Plant, or by enabling Destroyers/Missile Subs, since those would have the power to actually destroy buildings while bypassing the defenses. Either way, the Soviet Sub Pen Flametower has to go since Attack Subs currently can just camp under it's line of fire and be essentially "safe". Under is currently one of the only maps that you know nearly for certain, is going to last until the time limit expires, and there is little you can do about it unless the skill difference in teams is big... Which is something no map should force upon players to go through.
Complex surprises me slightly seeing as when I am playing it, it's mostly Allied victories due to Artillery whoring from the middle of the map (raise your hand if you do this, o/). I'm willing to bet a lot of this comes down to team setup. This is one of those maps that suffers from high economic income however, meaning that the later half of a match ALWAYS comes down to Demo Truck spamming, which in turn contributes to the high base destruction victory numbers. This economic problem is largely at fault by the players not hunting Ore Trucks with infantry, since nobody ever uses the surface infantry passages (likely because it takes too long to destroy an Ore Truck with anything less than three Rocket/RPG's). Perhaps the base defenses near the Ore fields need to be removed, or placed where infantry attacking Ore Trucks don't get murdered by them. Despite all of it, I personally like this map.
Bonsai is honestly a mess and I cannot put it any lighter than stating that the Allied base needs a complete redesign. The War Factory is a V2 sponge and it always gets blown up very easily, while the Soviet one is both uphill AND in the rear of the base. The Radar Dome water backdoor should outright become inaccessible by being turned into deep water, and in general the Allied base could do with a few walls for some basic protection (if the Barracks/Silo and War Factory trade places, walls would be high enough to cover some of those buildings). Add to that, that this map is the worst performing map in all of Delta FPS wise (I'm sure it is due to the waterfalls being overkill on particle generation), and you can see why I conclude it to be my least favorite map. It is basically an inferior version of Zama (both maps use a similar layout).
That's all I really got to add at this time.