Alone vs. Co-op
I tried the experience bonus by leveling first couple chars alone and once I got to the Skeleton King my characters level were around 8-8,5. I also leveled couple of my characters in Co-op games with 3 other people with me. I ended up having my characters around level 7,5-8,5 by the time we downed the Skeleton King first time on those characters. So, the group experience bonus is about same as playing alone. The reason for lower level range for Co-op is because when people play together they move faster and sometimes different directions, so finding the right doors and places will reduce the amount of mobs killed per person.
I didn't notice any difference in amount of drops between playing alone and Co-oping. The reason might be that EVERYONE CAN ONLY SEE THEIR OWN LOOT, including gold, scrolls, all items, everything that can be picked up. Yes you heard right! If you kill a monster with a friend and he yells that nice legendary item and you didnt see it, that means the drop was only for your friend. So, no more ninjaing in games like in diablo2. BUT if you pick an item and then drop it back to ground, then everybody else can see it and pick it up.
Because of this new drop/looting system, there is no reason why Co-op games should give more loot, since the monsters have roughly 4 times the health when playing Co-op with 4 players to compared the 1 time the health when playing alone. So, there are 4 times more loot in 4player Co-op game, but every player can only see 1/4 of the total loot in 4 Co-op game, which is the same amount as playing alone.
Once you join Co-op games in beta, your follower isn't following you. But if you go town and talk with the merchant and tell him to follow you, he will follow even in Co-op games. (In the beta act 1 merchant, the templar, can be found south from the waypoint altar.)
Amount of monsters or their strength isnt increased when playing in Co-op games, only their hit points. The players damage output should be much higher when playing Co-op than alone, since for example demon hunter can give "Marked for Death" to increase everyones damage by 20% to the affected target or monk has various "Mantras" that boosts damage or increases defenses. So, if you have friend to play with, there are no reasons why you shouldn't. Thou, if you want to read all the lore and play your own smooth pace then you should play alone. There are no signi@#*#nt differences why you should or shouldn't play alone/Co-op.
Edited by Taistelija on 01/12/2011 19:00 GMT