Metal Mutation is a bit clunky and oddly designed, but it's got some solid play if you enjoy a top-down melee roguelite with a strong parry.
Let's look at your basic combat options. For defense, you have a mildly janky dodge and a very strong parry. A successful parry allows a special follow-up rush-forward attack (and you don't need to attack the enemy you parry), while dodge can be canceled into a kind of air combo. Your main weapon choice sets your basic combo and your cooldown special, and your basic combo can be interrupted by most other moves, which gets good use. Your secondary weapon choice (used by the floating girl) sets two more cooldown attacks (one which is especially good for more safely ending the dash air combo). You can take another very dramatic cooldown attack from bosses, which will depend on what boss you get it from. You've also got a running attack that you can do after you run a couple seconds, which tends to be an upgraded version of your basic. And when you get a finisher prompt, for some reason doing that is also an AoE aerial attack you can move and drop on nearby enemies. So you do have things to do as you fight.
You have six unlockable main weapons, and three secondaries. Your basic, special, main-secondary, and dash can each get elemental upgrades, which also may change their looks and properties. Any element upgrade has a first and second tier form, and some can be further upgraded with a second element (in very specific combinations that do not cover all elements). Element changes to your attacks help weapons get a little more varied than they initially seem. You also have an array of other upgrade options that can add properties and various random effects.
One definite issue with the game is that many of these other effects are patently terrible, and I mean "small chance to heal comically insignificant health with highly situational activation [i]and[/i] on a surprisingly long cooldown" levels of terrible. Another issue is that while the elemental attacks do vary, there are a lot of narrow, straight-line attacks and flashy AoEs, which do tend to feel overly samey beyond their graphics. The two element combination system also really limits your builds unless you abandon that altogether, and it seems like you have way too little influence over your elements to make focused builds work, meaning not fixating on the combinations seems to limit you without any way to compensate (there are upgrades that give you a general one-element boost, but you can only take those when you pass up the other upgrades of that same element, so there's just no way to use elements you are avoiding).
Another negative point is the co-op side mode, a set of just three non-procedural mini missions that just have no real interest, but that take a while and need to be farmed again and again. As you get stronger, these get easier to handle, which is good because the co-op aspect just makes no sense in the game. To enter co-op you need to be at specific points in your run and then find someone else also looking for co-op at the right time. In other words, you're not only bringing your own other players (because of course you are), but you all need to co-ordinate when your individual games are in a "can co-op" state, with huge power variations based on where you are in your runs. There's a way to do co-op from the pre-run base that's easier to co-ordinate, but doing that gives you a bunch of random upgrades that you can't even plan through (you don't get to choose between elements, you don't have needed rerolls, and you don't even know what you'll be offered as you build), so your build always comes out clunky, incomplete junk.
There's an oddball mix of metaprogression to work on, with weapon unlocks via currency, a stat tree built on XP, achievement-based weapon upgrades, and two layers of gearing. The first, you build up your gear objects for their slot bonuses, and then the second comes after the first clear, where you get another set of upgrades from enemy drops and slot into your gear (higher tier gear has more slots). These second upgrades also build up as you collect larger piles of their requisite drops, which makes this effectively a second stat/perk tree to advance. It's all kind of a lot, but there's kind of a nice novelty to it since it's not just flat feeding bonuses, and you get some small choice how you apply your options in the middling times before you basically have everything and are just piling on bonuses. There's also a token Hade-style piecemeal difficulty system you use to try and pull the threat side of the game up to match your power progression, but there's nothing really interesting there as it's still mainly raising enemy survivability and lowering your own.
All in all, I feel pretty positively towards it, even if it's a janky, half-baked mishmash of Curse of the Dead Gods and Hades. I like melee action with play options and parry-style active defense, and not many games lean into that properly.
