Wow! I've been waiting to try that game. I should be studying still. *grin*
I've just gone through my first adventure, and here are a few opinions:
The letters are way too small, I have some difficulty reading them. The interface isn't really like most roguelikes, but it's not hard to adapt. A lot of text in menus, coupled with the small letters make it hard for me to read them with ease.
Also, I haven't found an easy way to compare equipment, such as a simple inventory listing with the bonuses each piece offers. You can, however, access a text-based description with all the numbers in it, plus some more useful stuff. I'd still prefer to have an easy way to see quality/bonuses/numbers.
I haven't really had the chance to explore the inventory screen thoroughly, but it seems alright. Loads of places to put equipment, a little bit like IVAN, and some carrying locations too (belt, for example). Managing it is slightly clonky, because you can only swap items from place to place. It is realistic though, which is something I like... it appears you only have a limited amount of space where you can carry stuff (I did manage to bring some relatively heavy armour on my belt, so that's slightly weird *grin*).
Everything is slightly more awkward and less straightfoward than in most roguelikes (picking stuff up or looking around being an example). This isn't inherently bad, given the type of playstyle that Incursion seems to offer, but it would be really nice to be able to get what you want quicker.
Again, the font should be much bigger. Can't stress this enough. It's really hard to get accustomed to the interface when you can't easilly read all the text that gets thrown at you. And text is something you get a lot more in Incursion than in other roguelikes.
Even with all these slight difficulties, in my opinion mostly due to interface decisions, the game manages to seem pretty darn complex. Getting into a fight with a single enemy can and will be a challenge most of the time, and you have to be resourceful in almost all situations. This isn't the kind of game where you see a few (g)oblins and keep an arrow pressed 'till they're all dead.
I'm not much of a fan of the D20 system in computer games, because it was invented for un-aided play, only with dice. Computers can handle a lot more than that with no "overhead", so why not take advantage of it? I'm pretty sure regular D&D players should fit right in, even though the author says some modifications have been made to the standard system.
Now, if you'll excuse me, I have to go and try my second incursion!
P.S. Ah, yes, also, every room IS something. Not just a square space you can walk, as opposed to a single-square corridor, but a room that has some sort of meaning, and all sorts of items and furniture are placed accordingly inside. I really like it!