Synergies.

[whyBish]

And the diminishing returns on it ought to go as well. Each skill must have a reason to be pumped for its own sake (synergies are just a cop out). Or leave the dimishing returns, but give it another effect (like an underpowered "avoid" ?  1% chance per slvl ?).

I think it would be great if all skills in the game were under diminishing returns.

For example the Zon's passive tree is a great example with D/A/E/Crit Strike. You can easily put 11 or so skill points in there without feeling like you are being ripped off.

Another example would be some of the assassin skills(although she has too many one-point wonders). Fade/BoS is now nice since it stacks with Venom, death sentry doesn't need to be maxed to be useful, shadow master doesn't need to be maxed to be useful (although you investment is rewarded past level 12).

If a character has a number of skills that can be partially invested in under diminishing returns (and maybe a few mutually exclusive skills with constant damage that can be ramped linearly) then it is a whole lot more interesting. The main problem with this though is that there are two classes which are not designed to handle this, the sorc, and the paladin. The sorc pretty much just has different ways of dealing damage so will end up with 20/20 in one thing and 20/20 in a second element (with a point in teleport, and maybe some warmth).
The paladin is not at as bad a starting point as this, since he has one tab on ways to deal damage, one tab of auras that help with dealing damage, one one tab with protection. The problem for the paladin is that he can only use one aura at a time. I would fix this by making his main aura work for himself and his party at full strength, and any points in *any* other aura work at a discounted rate for *himself* only (perhaps a quarter?). The only problem here would be to remove the one point wonder effects from this (e.g. the knockback on sanctuary should only work if sanctuary is turned on), and redemption/meditation and the resist auras would all need to be scaled back to account for this (I.E. They were originally pumped because having them on involves giving up you damage aura)
Even a limited version of this would make it more interesting, but it would have to be cross-tree, perhaps pairing up one damage aura with one or more defensive auras and vice-versa?