First of all let me just say I think Searching for Group theoretically is a great idea but in practice I really don't like it. I know its a work in progress but still, I have seen it in another game and I just don't like it because if there aren't many people on it gives you a sense of emptiness and the user may be discouraged to start a new group or go solo a mission.
Also when a party is made, the conventional "invite" may be left aside because ppl might tend to wait till there is a 2 or 3 player party until joining therefore reducing the number of party's created which lowers the number of "invites" and weakens the community. Because every invite makes the receiving player feel "needed" or at least he receives attention which gives the sense of busyness and activity within the game. Also instead of looking up the friend list and joining a friend who is at an arcade depth you may be interested in or at a mission, players will start using the search party engine therefore reducing the amount of times you meet with the same "faces" then again weakening the community.
This may be a long shot but at least that is how I feel about it.

I am really satisfied with the current feel of the community, and regarding party's there is one thing I would change. When I have the "Join a Party" option selected and I hit "Start" at the mission interface I instantly jump into the mission Lobby because I once selected the checkbox which said "Don't ask me again & Create a Party when there is no party to join". There is no way to go back from this so it would be nice if the option "Create a party if there is none to join" would be a small checkbox under the "Join a party" button, therefore eliminating the need for a pop-up and giving players the opportunity to change the selected option if they ever want to.

On the monster side of things the new additions seemed great and the difficulty was pretty tough, still appropriate. It wasn't easy at least tier 3 and making the monsters harder like increasing the range of the bombie explosions or elevating the damage done by small knights is totally unnecessary. I was on a 2 player party and we both died a couple of times, then again we were a bit careless due to the unlimited energy but still the levels were hard but in a good way, not extremely tough nor easy so it does require some attention and skill to pass these levels.

I would add a station at stage 2 just because and probably a party button so that players don't get flooded by undead monsters while they are loading at the elevator.

Hope this helps and thanks for letting us test new features!