In some cases, customizations would have done the trick. In other cases, allied races were fantastic and perfect.
All of the allied races (yes, including highmountain tauren and lightforged draenei) were unique enough to be ideal for an 'allied race' with new racials. That said, more customizations would be nice. An example of a race that would have been a poor choice for an allied race, but can exist perfectly with customizations, are wildhammer dwarves. (I'd mention high elves as a customization for blood elves, but I fear that might rile people up)
I hear people arguing that "mag'har should have been a customization", but there are problems with this. First of all, the lore and sheer amount of customization behind all of the options for mag'har more than justify its own race. Second of all, brown skin orcs cannot exist as warlocks. Period. For it to be a customization would mean that that is possible, and that can't be possible.
Mecha-gnome complaints I do understand, but it's mistaken. They alter the animations of gnomes slightly and wouldn't make sense as 'customizations'. You can argue that the race itself is flawed and that's your opinion to have if you want it, but that's a completely different topic. They wouldn't work as a customization in their current form.
No other race should be even up for debate, but people are going to use any excuse to argue against them if they hate allied races so there you go.