Have been to The Haven about 4 times now, twixt Xmas and New Year. Why ?
Firstly, location:- Haven is at the entrance to Poole Harbour, one of the most beautiful estuaries in Britain, and fronts onto Sandbanks beach - a sandy beach walk all the way round to Bournemouth (or ferry to Studland on the other side).
Secondly:- we like swimming in the heated outdoor pool. Be warned that this involves (in winter) sort of freezing temporarily until you get into the water ... or you can wimp out and lounge around in the indoor pool.
At full rate the hotel is quite pricey, and attracts the 'Made in Chelsea' set who are best ignored. Look out for out of season bargains - this improves the value ratio !
We have been in various rooms over the years, this time in the more expensive sea view room which I found small-ish but modern. Great view though, and terrace; it is nice to hear the sound of the sea, and it was flooded with sunlight in the morning. In previous years we have overlooked the ferry (noisy), or had a family room over the Tennis court (spacious but boring).
Breakfast is a 'good hotel' buffet with fruits, ham, cheese and pastries in addition to cooked breakfast. One tip I can give you is to try the eggs benedict or florentine, which are delicious, but have to be ordered. This time we did not eat dinner in the hotel (other than light lunch at the bar) so can't comment on that, but in previous years the brasserie has been pretty good, and again the highlight of dining at the Haven is the view, including passing ferries at 'touching distance'. For a change this time we tried the nearby Cafe Shore, which is special, but pricey.
The way I look at it - a few days at the Haven makes a nice treat without the hassle and cost of flying somewhere - so why not ?