Stuff AVWW lacks is better reactiveness of entities (more detail of interaction between enemies, players and projectiles), more detail of character control (more momentum based movement, crouch walking, sliding, dodge moves, dynamic spell attacks (charge up spell power, movement affects spell power etc.))
(Note, when I say room generator, I mean generation of areas in general, outdoor, indoor, caves, et al)
Some of this is indeed "throwing new content" at it.
Some of it can be solved by introducing new mechanics and working them into the existing stuff (by no means an easy feat). For example, I would also like to see momentum becoming a bigger factor in this game, for players, shots, and enemies.
Also, aside from the human built rooms that get seeded every now and then, environmental challenges can be tricky as the positioning is random-ish. Sure, you can tack more interesting behavior into individual background-elements, but it is hard to do any sort of "positional" based puzzle. Though with more interesting ways the environmental objects can behave and interact, this sort of stuff may arise naturally in some generated rooms. (see below as well)
and less predictable world behaviour (Interiors in houses are completely not what the house advertises, monster are predictably always present in an area as in EVERY AREA, every biome and every house layout is always the same in terms of content despite the procedural generations, so its never a suprise what you will encounter next and it feels like it renders the fancy procedural generation mechanics obsolete or even annoying).
For making interior/cave areas more interesting, this has already been suggested quite often. Some of it is art (much of the art assets, especially in caves, are shared through all regions, making them look "same-ish"). Some of it is layout (the room generator does not have many different kinds of "cave rooms" like there are "building rooms"). Some of it is a lack of intelligence (like figuring out how to randomly create clever platforming or environmental puzzles, instead of the more or less "samey" way it tends to make parts of rooms). Some of it is a lack of variety (there aren't that many kinds of "room types" yet, IMO, there needs to be more)
And yea, making the room generator care about the building-type more is a good idea.
So yea, the room generator needs lots of work. (It's good, but more is needed)
Also, having more built-in human built rooms would help with this, and allow some of them to apply to caves and outdoor areas too (though special work will be needed to make them still feel "natural" even though they are human-built)
For the monster thing. Some of it is a lack of monster types. For example, skelebots in many places are "placeholders" for enemy types until more region appropriate enemies are created. Unfortunately, this gives the (somewhat correct) impression that enemy variety among region types is currently not very good, and worse gives the (incorrect) impression that this was intentional.
Also, varying enemy types by region or possibly even by "chunk"/room as well as by region type may help with making region uniqueness feel better.