Well, it depends. Guild Ball is definitely more thought intensive than
40k - it has the same level of decision and plan making that you might find it a game of Warmachine/Hordes, and manages to stuff it into a game with 12 models and a ball.
It's certainly not just basically soccer, as teams like the Butchers can essentially ignore the ball as they rampage across the table.
Team building is a little more nuanced than you seem to realize as well. You pick a Captain, a Mascot, and four other players, including a number of Union players (the mercenary faction). For a team like the Butchers, that means you can pick from:
Captains Fillet
Ox
Mascots Princess
Truffles
Players Boiler
Brisket
Veteran Brisket
Meathook
Shank
Boar
Tenderiser
Avarisse/Greede
Gutter
Decimate
Minx
Rage
Harry the Hat
So there's actually a lot of variety. And each model has around the same amount of abilities as a Warcaster/high-function solo in Warmachine/Hordes. Doing so much as changing a single model can drastically alter how a team plays.
The
rules are free and you can download paper dolls and card to play with before buying anything. And there's also the $70
two player starter set that's coming out.
Personally, I've fallen off the game a little bit. It's partially that trying to get to the group that plays it on Tuesdays is a hassle, a little burnout from playing a lot of games so far this year, and that the team I choose (the Masons) is one that players can learn quickly, but is kind of left behind when other players finally get a lock down on their teams' abilties. It also doesn't help that a lot of Mason plays, while hard hitting, are very obvious when set up.