It really depends on what character you play. Zane, for instance, has a lot of thinking to do for his powers, and a single item might change your entire world view on a build (like using the Big Boom Blaster with the Barrier).
On the other hand, Flak plays the same no matter what build you go. Headshot badguys, use Action Skill when the fight starts, rinse-repeat.
A good balance of the two is Amara. Knowing that her Brawl tree makes her indestructible after using her Action Skill, or that the blue tree dramatically increases your DPS when you do the same, is an important thing to remember.
- Gunplay-to-Action Skill: Flak, Moze, Zane, Amara.
- Easy-to-Complex: Moze, Amara, Flak, Zane.
- Melee-to-Sniper: Amara, Moze, Zane, Flak.
- Solo-to-Multiplayer: Flak, Moze, Zane, Amara.
If you're concerned about Moze's cooldown, consider going down her Demolition Woman tree. It's my personal favorite. Stay in the mech for a good 1-2 minutes killing enemies, hop out to have Auto Bear defend me for 15 seconds, use the turret I picked up from her machine gun tree to hop on Auto Bear's back and fire a minigun while Auto Bear tears it up. Each kill rewards me ~3 or so seconds off my cooldown, so my Action Skill is mostly back by the time that Auto Bear is finished. Make sure to pack the Iron Bear Barrier from the orange tree to make it a lot tougher.
After maxing out several characters, I've been giving it a break...until my friends got it from the Steam deal. I tell you what, playing BL3 with four players is a trip, and easily the best experience I've had playing the game. It was fun single player, but too predictable. With 4 players, the difficulty is ramped up perfectly so that players are consistently needing assistance without it feeling oppressive. I can't wait to hop back into it tonight. None of my friends have seen the Magnificent Moze just exploding everything with a permanent Bear mech, and I'm about to show them their new god.