We went to this restaurant on 11th August 2011 for dinner having seen the recommendations on this website and I have to say it was disappointing.
The location is lovely but we had to wait 20 mins for a drink and 1hr 20 mins for our main course to arrive (and we were not alone in that judging by other tables nearby). When the food did arrive, it was OK but that's all, at £100 for two with 1/2 a bottle of wine.
The waiting staff seemed a sullen lot too, with the exception of the maitre d' who welcomed us pleasantly enough but doesn't run a very efficient operation.
There are several restaurants along this strip and, having been to another one during the week we were in Ile Rousse, it may be that they all suffer from the same problem.
They are all effectively smallish chalets on the promenade which occupy large areas of the beach, and I imagine the kitchens are just not big enough for the number of punters.
We have been to Ile Rousse about four times now and like the place very much but I'd avoid La Marinella unless you are prepared to have an extremely slow, ordinary meal with glum staff. The location is very pretty though.