Sadras
Legend
what I feel is severely lacking:
• spell interruption.
Agreed.
• more rules to reinforce cooperative play
This was extremely evident in 4e, but why do you think this is necessary. Is it because sometimes players work against each other and as DM you prefer to encourage cooperative play?
• different ways to gain XP (not just combat )
I have never been a fan of the XP systems in any of the editions. I'm surprised how little they have elaborated on this throughout the years which is pretty sad considering how critically important it is for the DM and the players for different reasons.
Beside the obvious of how fast or slow the XP pace, I believe PCs should gain XPs for:
1) Gaining knowledge of a setting: Either through meeting important NPCs, traveling new roads/towns/cities, obtaining lost lore/history. This applies mostly to long-term campaigns.
2) Gaining magical or divine knowledge or through related experiences.
3) Intelligent, Comedic or Cinematic moments during roleplay.
4) Monster experience - could reflect a set minimum of encountering a beast and perhaps an additional amount for every ability the PCs experience. For instance a Dragon has an XP value of abc, but perhaps the PCs only experience a of its ablities why should they get the full total.
Perhaps the party only had to deal with the Dragon's tough armour, strength, breath weapon, bite and claw and missed out completely on its spells, flight, wing buffet, and tail slap and any other supernatural abilities. They do not necessarily deserve to get all the XPs then since they have learnt very little of a Dragons capabilties.
I'm not saying WoTC should break down abilities for XPs, but a discussion point could be made for it. Its not game-breaking, just my personal quirk.
Then there is party XP as opposed to indvidual XPs
In our campaign I let the party all level up at the same time - I have lumped all their XPs required to gain a new level and instead have a party XP total. So for D&DN they are all level 7, i think requiring 9,000 for level 8, so with 4 in the group 4 x 9,000 = 36,000 XPs required. So if the mage discovers some historic arcane lore, and since he is part of the group, the party gains the XP. Therefore once they hit that 36,000 mark they can all level-up.
• removing the sacred cow of ability scores ( keeping only the modifier )
That is certainly an option. Lean towards the White Wolf system. If they could also cap/HP gain and then you have it. I think E6 and Pathfinder's P6 have got it right.