This is based on playing the beta for 2 hours or so. I'll post again after I play more this weekend.
Got my code Wednesday and played the beta for a couple of hours. Overall I liked it a lot. Everything graphically has a little more polish on it than the first game which already looked great. Character movement, handling and shooting is unchanged so you can expect the same level of fine tuned control. The big changes are in the sub-classes and weapon loadouts. The sub-class system appears to be more streamlined with less choices as far as abilities go. The first game allowed you to choose from different sub-powers for the same ability whereas now you just get the ability and whatever powers it comes with. They've eliminated some choices there, but I don't think it has to be a bad thing. You still have your choice of 3 grenade types and 3 jumps.
The biggest change I have seen so far is the weapon loadouts. You no longer have a primary, secondary and heavy weapons. You now have kinetic weapons, energy weapons and special (I think) weapons. The same weapon types (scout rifle, auto rifles, hand cannons etc) can be kinetic or energy weapons. Your special weapons are basically what used to be heavy weapons that use purple ammo, but the weapon types included in the special classification have changed. Most notably the fact that shotguns, fusion rifles and sniper rifles are included in the special category. Honestly I don't really like it at all. The purple (special) ammo does seem to be more available in both single player and MP than the last game though. They have also added grenade launchers to the special category but they don't seem great from what I have seen so far.
There is a playable strike in the beta that is a lot of fun. They have added in named enemies that are sort of like mini-mini-bosses which bring additional difficulty to some of the sections, but still can be taken out solo with concentrated fire or special abilities. I really like that addition. Hopefully they will make them have rare legendary drops. They have also added new enemy types and changed the behavior and equipment of some of the familiar ones.
TL;DR- The Destiny 2 beta throws some changes into the mix, but it is largely the same game as the first. I am looking forward to playing it periodically over the next couple of years. Well worth your time if you liked the first one.
