Sheever's main weakness is when she's doing play by play during ganks/teamfights, it's messy, doesn't mean much and she isn't talking about the important stuff(or missing it). Also her voice is pretty annoying but it's not that bad imo, some people dislike it a lot. On the plus side, she puts a lot of effort into casting every game possible and often is the only caster on it seems.
Ayesee's voice is good but yeah he never stops talking and say the most pointless shit ever. At least he gets usually get Draskyll to commentate which balances it out but Draskyll has been losing his touch lately I feel, makes a lot of innacurate statements especially about team's playstyles or hero picks or whatever, like he's not following the scene very closely.
Epi is fairly terrible but he's gotten better a bit.
All in all they're not super good casters but they do fine if they have good co casters. Which is NOT Reesion, god, if I wanted to listen to a 14years old not talking about anything useful I'd play cod. Not a big fan of EternalEnvy either, do love Merlini, Puppey, Synderen(back when he was casting, now he doesn't really anymore). Paintitgold and Wagamama were pretty good too.
Unrelated note but if you've not been following Reddit, the website for frostivus has been updated everyday by Valve with new stuff. It started by having more greevils in the pictures, and then the presents disapeared and now the website page is basically completely destroyed with a hidden message that says "We haz ur prezzenz" and "u waz rob". Pretty fun stuff.