Pressure and hours I would say are not very different. Possibly more even in a large, full-service environment (longer projects) and spikier in a smaller/strategy firm, but on average it is what it is. The "feeling" or culture of companies will be very different - even from one full-service firm to another - and I think that's probably your best guideline as to whether you are going to enjoy the experience.
Full-service firms are definitely more structured and methodology-rich (or methodology obsessed, depending on your PoV), although some strategy houses are also framework and methodology rich (but there is a qualitative difference - one is a framework for delivering a given solution, the other is a way to devise a solution in the first place).
Type of project depends on what the firm collectively actually knows, but if you want connections to R&D to leverage your experience (not necessarily to work in R&D, but to add more value to the client and your pay packet!), much work in full-service firms tends to be IT/systems-oriented.
For "outplacement" options a few years down the line, the first rank strategy firms are difficult to beat, but then they are correspondingly difficult to enter in the first place.
A specialised firm may allow you to use your existing knowledge (I assume you are not going to join as a partner and start up a new practice area!) and to pick up an understanding of how other functions or industries work, and these are generally well-connected firms that can help you finding an industry position, albeit usually at lower levels than strategy firms.
Beware of going too small or too obscure if you want to switch rather than stay and grow the firm. It may well turn out to be a cul-de-sac with little option but to backtrack.