Wait...melee units in an RTS? Maybe I'm colored by my TotalA/SupCom background, but melee units sound like a big suicide unless it's a hulking behemoth of bajillions of HP (see Ultralisk) and even in Starcraft those are terrifyingly fast. Goo doesn't seem to be that kind of game, so the lack of melee doesn't bother me in the slightest.
As far as the gameplay, well Beta and Human are similar but I don't feel they PLAY similarly. Beta can expand wherever they freaking want, while Humans are stuck with ONE base, and a fragile one at that unless you build really cleverly. The Goo seems borderline overpowered if you are left alone by your opponent, but I can see how they would be very vulnerable to early harass (probably why the Formless Goo can defend themselves in melee). Goo also lacks ANY air power, as far as I have seen, so the key to keeping the Goo down is constant harassment, preferrably by air. But I've only played two skirmishes against the AI yet, so don't look to me for expert advice.
I dunno, the game is fun so far. But due to the lack of unit variety (there's 3 units in each class, so something like 9 units per faction) I can see the game eventually growing boring and stale. I do hope that the developers continue to balance and develop expansions. If they keep up, this game could definitely last. So far I like it a lot.
But do mind this is after just a few hours of skirmishing. And also mind that TotalBiscuit said straight up that the game has its flaws, but it's the best RTS to come out in YEARS (including Planetary Annihilation...man what a disappointment that was
) so I think it definitely has potential if cared for by the developers. Otherwise it's probably a good 20-30 hours of fun before it grows a bit stale. I'll keep play, personally. Especially the campaign, even though Skirmish and multiplayer against friends was always more my thing.