Part of why shoot 'em ups are great is explosions. Massive fancy explosions everywhere. Kerblam! Foosh! Splode! Tower defence games are also great at spewing fire, debris, and particles: that's how you know you've defended that thing real good. Sprang! Clonk! Fsssh! Combine the two and you'd surely have fire, lasers, missiles, and explosions just everywhere. Looking at Excubitor shows yep, that's about right. The shmup/TD has come to my attention by popping up on Steam Greenlight, but it's got a public alpha version we can play right now too. Blammo!
I had a quick bash and it's pretty good fun. It's the usual wave survival thing you'd expect with a tower defense, only blasting enemies in your fancy hoverspaceship is just as important as turrets.
You can't cover everywhere, or they aren't strong enough to handle it, so you zip around from wave to wave throwing bullets and missiles. Some levels have activatable traps as well, like giant spinning deathfans placed in a canyon because reasons. The shooting's a mite finnicky though, with point targeting than the usual shmup indiscriminate stream of bullets; I'm not sure why. You ship has two two weapon slots to fill with deathblasters of your choice too. And has a nice bright blue afterburner dodge. I like that ship.
The demo has a tutorial then a hearty number of levels. It's a nice spot of fun on a Friday afternoon.