I think Shaman could definitely stand an overhaul. Speaking from a former Resto PoV, and looking back on it from my MW and Druid/Pally ults, it's clear that several important parts of the class either conflict with each other, the kits of other classes, or the content (repeatedly).
For example, I find the Shaman Mastery to be a relic of the Cataclysm beta when Blizzard was so sure that people would stay at lower levels of health for extended periods of time. That quickly faded away in PvE, yet it remains strong in PvP to the point that Blizzard seems actively afraid of offering Resto any meaningful PvE buffs despite their current state of being dead last in just about every fight of the ToT tier, even in their "stack healing niche". It needs to be revamped so it isn't so polarizing, restricting one at the expense of the other to this degree is not ok.
Speaking of which, their niche absolutely fails to manifest itself in-game. Shaman despite (usually) being functional in stack healing encounters, never "shine" on them: some other class is always competitive/beating them in those situations. Considering how heavily they drop off in movement/spreading encounters, I find this a penalty, not a niche. No other healer suffers so much for such common raid mechanics. It doesn't help that Resto had almost the exact same problem an expansion ago...what was all that MoP development time for, exactly? New CDs to blow during CD time are nice, but is that really the best they could do? I don't think so. The spec is tied to Healing Rain so thoroughly now it's little better than the Chain Heal spamfest of WotLK, and thanks to the content/functionality with other healers and HRain's weaknesses, it ends up largely being overheal. So they just seem to gem spirit so that the other healers can do their job better with MTT and the occasional CD. Progress?
And even though this isn't exclusive to Shaman, I find their talent/glyph selection atrocious. Shaman were the last class to receive their talent tree data, but you can't tell where the extra dev time went. Same with major (and especially minor) Glyphs, i've seen more thought put into the graphics of a Stormwind City bench than the art/effects accompanying those Minor glyphs put together.
TL;DR: Shaman don't necessarily need a complete overhaul so much as they just need actual Developer time and a clear direction that actually matters/is apparent in-game. Their kit feels like an expansion behind the times, and Resto (seriously) got more "tweaks" the last couple of bandaids than they did for most of the MoP beta. It's showing in their performance, and Blizzard's work on addressing the spec have, quite frankly, been embarrassing. They deserve a lot more crap about it than they are getting.