TL;DR: Rather simple cartoonish inoffensive tower defense game. Martians are coming and you must use a bunch of mechanical contraptions (fridges, grills, ...) to stop them from abducting the cows.
I've played this game for about 14 zones in Veteran mode (Summer, invasion 4).
BPE takes some cues from Plants vs Zombies: having to click currency icons to collect them (cogs in BPE), cartoonish visual style with rather silly enemies (Martian maids, crazy scientists, ninjas, ...), pre-mission selection of towers, no tower upgrades, a chance to look at the enemies in the incoming wave...
The biggest difference is that the Martians move along a single route, from the crop circle to collect the cows at the pasture, after which they will haul the cows to the circle to be abducted. In this sense, it's a bit like Defense Grid: dropped cows will (slowly) walk back to the pasture.
With no actual tower upgrades, after placing the towers the player ends up mostly using a ray gun to cause additional damage to the enemies. There are some enemies that actually need player input to defeat (energy shields, ninja Martians who replaced themselves with logs, undercover Martians), but together with the "need to click the cogs to collect them" mechanic feels a bit like a means to give the player something to do. There hasn't been a chance of designing the enemy path (mazeing) either.
It's inoffensive, but nothing spectacular. Just get Plants vs Zombies or Defense Grid instead.