For me, the lack of appeal wasn't in the gameplay, the graphics or anything such. It was point. Why did this exist? What was the purpose of the game? Was it just to kill robots for the fun of it? Was there any progression at all? Was there a deep and interesting combat system (A la Dark Souls) to keep me engaged? Was it a puzzle game?
I could never make out what it was about Raptor that was supposed to get people, and once it released on EA, I still couldn't find that "thing" that is supposed to carry the game. I'm not the sort of person that buys Goat Simulator just to fool around. I see no point in that. I need a game to have a clear purpose. Raptor seemed, to me, to lack that.
This to be honest is what I personally was worried about, though I didn't really speak of it much; the sudden leap into EA at the time it was done seemed like a "cant avoid it" thing, after all.
The problem to me is the state the game was released in. It really doesnt seem to have a point other than smash things. The real meat of things just wasnt there yet. What it was supposed to be was the game constantly putting you in all of these complicated tactical situations versus the robots; the sorts of situations where you were going to have to think your way out, and do things like lure the robots into specific positions, or use their talents against each other... you werent going to be able to just smash them by leaping all over the place.
All of the bots were designed with this in mind. They have concepts and mechanics unique to each that would mingle together in interesting ways, and when combined with the terrain, would make complicated stuations for you. For example, one bot was something that ran on the ground, and would charge at you like a bull; when it hit an obstacle, it would spray tons of fast bullets in all directions; you would want to hide behind something when it does that, and then attack while it's stunned. Another bot was one that had no attack of it's own, but instead had the ability to pick up other bots and throw them in your general direction, getting them close to you fast. So, room idea: a tall room with a central pillar, and a platform up above. The thrower bot starts grabbing those chargers and dropping them down onto the player, who has to react to their position and use the pillar to take them out safely as they keep landing.
That's just one example, but that's what the gameplay was meant to be like. All sorts of room ideas were possible even just with the bots that are currently on paper. Helping to come up with bots and then placing them into positions in rooms to create these situations was my part in this. But while the bot concepts were made (as well as traps and various things the player would interact with), it just didn't get far enough along to show off any of that stuff. The version of the game you've seen just plops the occaisional bot down randomly.
My opinion of the game having high potential is still the same, but even I cant deny that it just wasnt in a state where it could REALLY be shown off for what it was meant to become. In such an early state, it did seem mindless. But if I recall, the situation was that it *had* to be stuck into EA because time was up, so.... yeah, nasty bit, that. The whole situation sucks... very frustrating.