Playing Skul was a little frustrating to me. It's got some nice pixel art and the roguelike genre is ever-popular, but beyond that impression, there simply isn't much to be found here that other games haven't done better.
Combat consists of fighting common enemies, minibosses, and bosses. The common enemies aren't particularly interesting - there's not a lot of different types, and many of them (particularly the sword grunts) just sit there stunned as you mash an entire horde of them at once repeatedly. In later areas, some of the enemies are more interesting, but many of the enemies are also just slightly stronger versions with almost the same moveset. More variety in each area would have really helped these sections feel more interesting. Besides that, there is no procedural map generation - all of the maps are premade and you'll quickly see all of the layouts of them.
The mini-bosses are slightly more interesting, as there's 7 of them, and you fight random ones each time! Unfortunately, the later areas use the exact same pool of mini-bosses, except you fight multiple of them at once. The bosses at least are more interesting, featuring terrain, large and dramatic moves, and interesting boss phases.
Skul's namesake mechanic is the ability to pickup and upgrade Skulls, which give you new movesets to use each run. In principle, this is quite neat - the skulls tend to play pretty diversely, featuring different attacks, abilities, and dashes. Skulls can also be upgraded in rarity during runs. The only criticism of this mechanic that I have is that it's often unlikely that you'll upgrade the Common skulls to this point when the skulls that start at Unique give you such a massive headstart on how much currency you need to upgrade them.
Skul also features a relic system, like many other roguelikes, with two differentiating features: you can only hold nine total, and they also have traits that activate if you have enough of each. I feel like the game simply has too many traits, as I never felt the desire to chase traits over just getting the flat stat boosts (like bonus damage or health). Additionally, unlike other roguelikes, you get no choice of your equipment often times - clearing maps that reward equipment just gives you a random piece rather than a choice.
Lastly, Skul features a meta-progression system where gathering Dark Crystals grants you upgrades. I really dislike these systems when they offer you objectively better stats as it makes you feel like you're wasting your time on grinding runs until you have your stats fully maxed. The difference of dealing 60% more phys. and magic damage, bonus max health, and a revive per run is so massive, but it'll take you tons of grinding to get to it. I would've enjoyed an unlock system instead of this.
Ultimately, Skul is an okay game, but I can't say that I would recommend you play this versus any other action roguelite out there. I hate to say it, but Dead Cells simply feels like an objectively better version of this game, having a better progression system, procedural maps, better enemy and boss variety, and smoother combat.
I'd give Skul a 4/10. I would only recommend this to people who can't get enough of Dead Cells and simply want more content to play.