Stayed here for first time a few weeks back as it was much cheaper than T4 Hilton & I was flying from T5 (although its nowhere near!
Its OK but I still much prefer Hilton T4. Rooms there are more contemporary/pleasing (although much smaller) & overall I much prefer location, ambiance & facilities at T4.
As for calling this place Hilton T5 - what the ****?!!
I just don't get in what world the rooms at T4 could be better than those at T5, the T5 rooms (and bathrooms) are about twice the size, better laid out and with baths (not shower only, which is all you get at T4 even in their presidential suite). Even after the refurb at T4 the rooms feel cell like and compromised. Only the Renaissance comes close amongst upper end full service hotels at LHR remotely similarly awful basic rooms.
I do quite like the T4 and if the poor lounge service at T5 continues then that is probably going to push more business there way but I don't like the gym there much and unless you get a suite the rooms are unacceptable at the price point compared to the very good competition.
I think bars and restaurants are a wash at both properties and if you are travelling with any luggage you probably need an uber to reach both too.