I know you guys are going to work on Horde mode at some point, and I have a few suggestions. Currently Horde mode is long, tedious, boring, and fairly difficult in later waves if you don't resort to cheesing the AI. I think borrowing a page from Killing Floor 2's book would fix these problems;
-Less enemies at a time. Waves are broken into mini-waves, so you aren't overwhelmed, but still kept on your toes. Instead of fighting 60 men at a time, you'll be fighting a constantly-refreshing 20 or 30 at a time. This would reduce the amount of kiting necessary in order to survive at later waves. Kiting is f**king boring to watch and it can take way too long.
-Fewer, but larger waves. Instead of 21 waves of 60 enemies , how about 10 waves of 120 enemies? If you break them into mini-waves (as noted in the previous point), it won't be overwhelming, and won't take as long, since less kiting will be necessary.
-Smaller Arenas. For example, on Feitoria, instead of using the entire map, restrict the play area to inside the castle walls. Massive maps take forever to traverse, and there's plenty of places for AI to get stuck. We don't want to drag waves out unnecessarily. Smaller arenas are also better for smaller, refreshing waves.
-People joining on later waves should get more gold to spend, or let us drop them gold so they can gear up.
-Player spawn should have all (or at least most) weapons and armor available. having to run across the map in between waves to get what you need is tedious and sometimes means you get your item as 15 enemies spawn next to you. Getting headshotted by a longbow as the next wave starts because you needed X item is counter productive.
-Boss enemies (great mauls, Ogres, Seymour) could use some work. I don't know exactly how to fix them without neutering them completely, but they shouldn't be able to damage you through your parry. We should be able to fight them with melee weapons, in my opinion.
-Speaking of bosses, it would be cool if we had more than just Seymour, if there were several "big bad" bosses to choose from, and we got a random one at the end of each game. More Variety is always good.
That's all I can think of for now.
EDIT: I thought of another thing. Bonus objectives. Accomplishing a certain task during a wave (King of the Hill, or push the cart) for bonus cash/gold, and experience.