I stayed at the Radisson Blu for two stays during August while dropping off and picking up my son in Biarritz. The hotel is shockingly expensive for the quality of the rooms. I had wanted to stay at the Hotel du Palais, but they required a minimum stay of 1 week during the summer.
The rooms resembled a standard Marriott / Holiday Inn. The air-conditioning was inadequate for the room (e.g., not strong enough to cool the room down). The hotel has an Elemis spa, but the toiletries in the room are not Elemis. They allow dogs to stay in the rooms (big dogs). There is parking at the hotel in an underground garage at 20 euros per night.
On the positive side, the breakfast buffet was comprehensive and I dined at the rooftop restaurant one evening and that was acceptable.
I would not return to this hotel again, as the room rate was just completely out of proportion to the quality.

Hotel was nice, room was really large. Very convenient for walking back after dinner or drinks out. Parking very expensive, moved Car after 2nd day to park in road behind the hotel for free. Pool was nice and not too busy. Tried to get a drink on the roof after 11 but it was closed might have better hours in mid summer though and there are plenty of alternative places to get a drink around the hotel. Door staff on all night so easy to come and go late at night. Tried a really nice tapas bar just down the road, think it was called the Basque Bar. Dont look at anything in the fridge, we moved some stuff to put some of our own water and it charges you (although easily sorted out with reception) Supermarket just down the road which we used for some bits in the room.

We recently returned from a 5-night vacation in Biarritz with my wife and three young children. We all stayed in one room, with two queen beds and a (free) cot for our 8-yr old. We had an ocean-facing view in what was a fairly standard, but well-equipped room. The highlight is definitely the pool and lounge/bar. We would come back from a day trip -- to San Jean de Luz or San Sebastian -- and have a swim and cocktails. The view is sensational. The staff could not have been more friendly. The concierge helped us locate a babysitter, a doctor to treat one of our kid's ear infections, and even concert tickets. The breakfast, while a bit overpriced, was very good and free for our children. Finally, the location was fantastic. Of the two main beaches, the Cote d'Basque was far more preferable for us: it was much more low-key, less touristy and within walking distance of everything, including two great finds: a beach bar called Les 100 Marches and a great Italian restaurant called Il Giardino (see separate reviews). This isn't a 5-star luxury hotel, but it was more than suitable for our vacation and I'd recommend it to friends travelling to this beautiful part of the the world.

Hotels in the summer in Biarritz are expensive! So be ready to pay up. I paid $165 Euro for the Radisson Blu (by using their 25% best price guarantee discount). So you can see what their rooms cost generally. Rooms were very large and bathroom was decent sized, especially for Europe. Beds are nice in comfy. However it's decorated in that tacky beach style decor (blue pastels, etc.).

They have a nice roof deck with bar and restaurant overlooking the city/water, with a pool too. They claim the pool is heated but the water is quite cold and the areas for chairs around the pool are very small.

I liked the location however note that they are not near the beach (even though it looks like it). The area where they are has a beach only in low tide. If you want to be near the beach, you want to be between the Port and the Lighthouse - that beach is avail all the time.

From a value perspective, I don't think its worth the price - but comparatively speaking during my stay it was one of the more reasonably priced hotels (amazing that!), so if that is also true when you are booking, it's worth the stay.