Risk of Rain has great core gameplay mechanics. It's a platformer/roguelike where you pick a character then need to find teleporters to get back to your ship without dying. There are tons of items you can randomly find during your journey, each class has different abilities, there are tons of unlockables / challenges, the game is pretty difficult but rewarding and I really love its style. It has, however, a fatal design flaw.
I'll just start with the show-stopper, the maps are too big, your character moves too slowly, the action is too dispersed. Maps are huge in Risk of Rain. They really should be smaller, a lot smaller. When you're looking for the teleporter, you have no idea where to go, there's nothing more frustrating than arriving at a dead end and having to walk painfully slowly the other way and try another path. These ropes take forever to climb, these empty stretches of map take forever to walk through. And it's just boring. I know that one of the features of the game is that it gets progressively more difficult, on a timer, but just make the time needed for difficulty increases shorter, and make the maps like, a tenth of their size.
And I say that because the core gameplay is good. Fighting is good, finding items is good, even if chests contain these items and you need money to open them - you also need money to repair drones - and you don't get money up front - worse, you lose all of your money at the end of a level - so if you start a level and there are a bunch of chests where you are, you'll have to walk all the way back to open them, why not let you carry your money forward? Just increase the costs a little to balance for that. Items have a ton of uses, healing you when you deal damage, fearing enemies, making enemies explode, shooting mortars, missiles, huge saw blades, making clones of dead enemies, healing yourself over time, increasing your attack speed... And it's random each time, you might find a set of items that'll make it easier in one run and harder in another. I really love how you unlock new items by completing challenges.
And I'm bothered by all the content in this game that I'm never going to see because there's just no fun in 80% of it. You find the teleporter, then a boss spawns. Bosses are really huge and dangerous and while you're fighting them, enemies come in constantly for 90 seconds. After that, you have to kill all enemies on the map before you can live. I hope you didn't leave an enemy at the beginning of the stage because you'll have to walk all the way back to kill them. Just despawn enemies when you get too far away from them and spawn them closer to you, that'll cut down on some useless walking.
I've only unlocked three classes and they all play differently - and you have specific challenges for all of them. You have four moves, they're all more-or-less the same, there's no concept of "mana", it's all cooldown-based. I kinda wish you'd see your stats better, what's my base damage? HP regeneration speed? What are the effects of the items I have on myself right now? It's not like this was unavailable info, you can see all of this in the item list page, why not surface it when needed? Fighting monsters is tough, but fair, you have warnings for most attacks and you can jump, roll, smoke bomb or shield out of the way. Enemies are varied, from melee slow opponents to laser firing lizards to gigantic golems, there's a lot to hate.
I really want to love Risk of Rain, but I can't, even if the fun parts are 100% fun, they only make about 15% of the game, the rest, I feel like, was pointless walking around and being bored. Too bad.