i think they're cute! i love sci-fi settings (i played a ton of xcom, slime rancher and trials in tainted space) so whenever slime species get included in the universe i get a little giddy. i especially love it when there's an in-game codex for the species and how they work.
sexually? they don't really do much for me unless they're shaped like people. i also don't like the whole "getting engulfed inside someone's body" shit, which is prevalent in tons of R34 slime stuff. starbound has pet species of slime bats and slime blobs and they're my favorites! i think i just like slime in general because it reminds me of jell-o