Honestly, most of the points are simple skill issues, and possibly not being willing to try things out.
A lot of enemies can be taken on and controlled at once, when you know how. Positioning and cooperation is key here. Leveling is boring and… Unrewarding? Really? In VT1, the only thing you got from leveling was two trinket slots. That’s it, there were your rewards. Here, we have new careers and Talents for each of them. And Commendation Chests. Quite a lot more rewards there.
Talents and their values are somewhat questionable, true, but there are some surprisingly good ones. Especially once you start trying out more exotic builds. Some Career Skills take figuring out to use effectively, but once you do, they are very effective at what they do.
Exploring may be somewhat pointless once you find the book locations and a few better-hidden chest and other resources, but Veteran (and Recruit) has quite enough of everything sprinkled about to indeed make chests somewhat redundant.
Ranged weapon use underdeveloped…? Sorry, can’t figure this out. Ranged combat is still dominating the game, although slightly less than what it was. That said, this was never intended to be a shooter game. Melee is supposed to be the primary combat form.
Junk items… Well, inferring from your comments, you haven’t gotten to that high a level yet, and that means low Hero Power and low-quality items. So they will get more relevant. If that means item Properties and Traits, there indeed is disparity, but only very few of them are really useless. (I can only really think of two useless Properties, and even one of them might be useful in highly specific situations.) The percentages might seem insignificant, but those 5 and 10-% adds stack up, and even alone hit some significant points. Drop rates for higher-quality stuff improve as you get to higher character level and difficulty, but some rates will stay quite low. Loot is a means to an end, not an end in itself.
So, in the end, I think you and your friends need to invest some more time here, and start testing stuff to find your fun, or find a simpler and faster-progressing game instead. I might toss a recommendation on the co-op Warriors games for simple Hack ‘n’ Slash, but there are a lot more options. Simple, this game is not.