Rotel have a VERY good reputation here in the UK, much higher regarded than Cambridge Audio for example, and for good reason, if you hear them side by side, then most people seem to prefer Rotel by a LONG way, at least in this country.
Their house sound is somewhat different to most of the other mainstream manufacturers though, which can lead to a love/hate thing. They are typically bright, fast, punchy and very lively components, regarded as a sort of "baby Naim" type sound, especially in the case of their most recent stuff, like the 02 series and the old 97x series.
On the other hand, another brand which seems very popular on this board, Cambridge Audio, is regarded as quite poor in the UK, being sold in a shop called Richer Sounds, well regarded as being for entry level hifi only. I used to own the A500 amp and found it flat, lifeless, muddled and lacking in detail, and is not in the same league as a Rotel for example.
Its definitely safe to say Rotel are more than likely to be on of the 3 most popular brands of hifi in the UK, at least speaking to people who work in shops seem to suggest that to be the case.