Bloons Super Monkey 2 and Empire Warriors TD are both currently free on the Playstore for them that want them.
BSM2 is a cutesy non-violent shootemup that is actually quite good. A fair few different weapon options with good power scaling, a few different character types, no energy/stamina system, but there'll be a fair bit of grind to get everything unlocked and powered up. Currently on world 2, and have enjoyed it immensely so far. Tiny bit of a problem in hitting my back key when down the bottom of the screen, but that's on me, not the game. Plenty of powerups, plenty of weapon combos. Just an enjoyable little shooter, that would even be fine for kids (though there's a fairly high skill cap too). I went Dart on left, Boomerang on right, and a Magic core to begin with, and was pretty happy with it. Now levelling Beam core instead for more forward firepower. Doing Ice/Magic/Ice core on Ice Monkey, just to try him out. Oh, and don't worry, you're not stuck with Ice Monkey in world 2. As soon as you defeat the Yeti (6-12 lvls in) you can switch him back out for Super Monkey. So don't waste your red thingies if you don't want him.
Empire Warriors TD is a tower defense game with hero based cooldowns. It seems quite competent at what it does, though I'm not a huge fan of the genre. You also get a free, fairly good hero during the free app event, so now's a good time to try the game out.
But yeah, get BSM2 at least. It's pretty good (though admittedly, I just like shootemups. But this is a good one for mobile).
Had a bit more of a go at Chimera Recollect. Got 31000 gold collected from downtime, so bought *all-the-things* from stores. Wow did this just get easier. Trying out the Water head. Damn lasers are great, even if they're a little MP intensive. But with a Cloud(R) tail, it's still unlimited laser death for everyone. Probably even better than Dragon fire. Zap! Nothing left. Really am trying to use other tail types (Skeleton shurikens look cool, and might be feasible at a high level, considering you start with 4, so hoping it goes to 9), but unlimited MP from cloud is just too good. Trying different bodies too, but so far everything feels weaker than Butterfly (R)'s glide and penetrate. Heavy kinda does very little IMO. I'm really just trying to not waste all my XP by levelling other stuff for now. Lizard's my best HP tail, but I need something better for life restocks.