The problem you have with trying to categorise such diverse cuisines together is that obviously, and wonderfully, they just don't want to fit into your neat boxes. I love the idea of the four cuisines on a stage like a boy band; Sichuan, as the 'kerazee' Robbie Williams is spicy, punky and unpredictable, Cantonese Gary Barlow, gloopy and ubiquitous, for many years the only one that you'd find anywhere. Prissy Mark might match Huiyang, meticulously turned out, perfectly prepared and delicately flavoured, leaving Jason or Howard to stand in for Shandong's background soups, seafoods and, um, harmonising melodies.
Going by this broad categorisation, you might worry that setting up a Hunanese restaurant round here would be like throwing an ultra spicy tattooed powerhouse into the refined part of Pimlico that sits just off Sloane Square and forcing them to hang out with bankers, diplomats or the wives and mothers of such. It's not ideal.
Thankfully the joys of a generalisation (and particularly of my very stretchy analogy) are that you have plenty of room to work. Hunanese food is not the same as Sichuan. Not close. Despite the categorisation, the spice, where it is used, comes from the vinegary sour of pickle and ferment and not the numbing heat of the pepper. This doesn't mean that it's not hot at times, but the gulf in style is substantial.
As well as the differing cuisine styles, there is a different ethos to Chinese dining. In several of the cuisines, emphasis is given to the structure and composition of the meal you are eating. Individual dishes shared by the party might be individually underpowered to give harmonising notes or emphasise other elements of the dishes but by and large, you are tasting a whole orchestra, not eating a cellist.
It's in this last that Hunan's individuality comes out. Many Chinese restaurants will offer a group set menu intended to give an array of flavours. Hunan has nothing but a set menu. You pays your money and the orchestra plays. Solicitous staff check that you're not allergic or alarmed by any of the ingredients in the menu and from there you have a two hour roll through 18 or so courses. As most were no more than a bite, this was nowhere near as much as it sounds.
The problem for me is that nothing really stood out. I remember a couple of interesting dishes; a brown sauce soused beef tripe was uric and hearty, prawns, featured often, excelled when combined with a thick herby stuffing and crispy, salty, garlic and chilli green beans with a light tempura batter were excellent, a Dr Jekyll to its firey Sichuan brother. Other than those, I remember little, even on reviewing the menu two days later. I know what I ate was pleasant, we left nothing and murmured assent often, but the abiding memory was of background and filler. The orchestra were competent, but I couldn't for the life of me tell you what the soloists were like.The staff were multitudinal and solicitous, the ground floor terraced room narrow and cozy and despite the toilet facilities being a little more Chinatown than Sloane Square it's difficult to pick holes with the set up. A good spot for a business dinner or lunch and a fairly good call for a classy date, just go for the light chamber orchestra and don't expect Robbie Williams to show up.
Further reading on Chinese cuisine:http://redcook.net/2008/02/27/the-four-unique-schools-of-chinese-cooking/