I upload this image a lot, but I think it's particularly relevant to detail the cries of praise for Cortex Command.

The AI got sick and tired of trying to navigate my death-trap entrance tunnels and decided crashing right on the $(@! through my roof was the preferable solution.
Even with insane amounts of funds that remained the most grueling, desperate combat I have ever partaken in. Supplying new units was near impossible due to the huge amount of surface dwellers, and all of my rocket-capable tunnels had long since been collapsed.
Skirmish of course, has you fighting off a never-ending onslaught of enemies. Though you could engineer a spectacular defense, eventually every last stone will have crumbled, and the floors replaced with the mangled bodies of friend and foe alike.
... and moving on ...
You said you hated Tower Defense and I never tried this specifically but it's the only other thing that springs to mind. A very new Roguelike based on Crawl called Zot Defense.
http://sites.google.com/site/crawlvariations/Zot Defense is a tower-defense-styled variation on Crawl. You begin on Zot:5; monsters are generated in waves, swarming in from the upstairs. You must prevent the monsters from reaching the Orb of Zot, which you may not pick up or apport. During each turn in which a hostile monster stands over the Orb, you suffer one point of rot damage. Each time you go up one experience level, you receive a new special "Zot ability" which will aid you in protecting the Orb; the use of these abilities expends experience points from your XP pool. The waves of monsters grow in strength over time; at the end of each wave, an out-of-depth "boss" monster is generated. Every few waves, a rune is generated on the stairs along with the boss monster. You may pick up the Orb, and leave the dungeon with it, if you are carrying fifteen runes.
Fair winds!