Thomas M.
Yelp
Not just one of the last remaining warships of its era, but one of the most important as well: The HMS Victory is a must-see attraction which is part of the tremendous "Portsmouth Historic Dockyard" experience (along with the HMS which offers several days worth of HMS Warrior 1860, the HMS M.33 and the WWII submarine HMS Alliance, plus several museums) which offers several days of exciting sight-seeing for adults as much as more the smaller fry.
First things first: If you want to do all of the Portsmouth Harbour attractions in one day (better make it the full day, i.e. 10 a.m. to 5.30 p.m. in the summer and to 5 p.m. in the winter), make sure to book the "all attractions" ticket *ONLINE*, which will save you money: E.g. the single adult ticket costs UKP 32.00 on the door, but just 25.60 online. The HMS Victory as an individual attraction alone costs UKP 18.00.
The HMS Victory is in superb shape (no doubt the result of extensive - and ongoing - preservation and restoration) and full of exciting details on deck and inside. Since the ship is not just fully fitted with historic cannons but also with all kinds of furniture, vintage tableware, hammocks, etc etc you will truly get an impression of what live on such a ship must have been like back in the day - minus sea disturbances, explosions and scurvy. The lighting is very low-key (I imagine it must have been even darker inside back then).
You can visit all the decks (be careful on those steep steps between the decks - it's almost inconceivable how sailors were supposed to run up and down those!) and photography is allowed everywhere in the ship. But because of the low lighting you might find it difficult to get sharp images if you only have a smartphone or a super zoom camera).
If you have any questions while you're exploring the vessel, there are several friendly guides on every deck who you can ask anything. Of course they're friendlier towards single ladies than to single guys. ;)
Since HMS Victory is only part of a large visitors' experience, if you're exhausted or hungry from your exploits there are several restaurants and cafés (sadly, no pub!) on the grounds of the dockyard nearby.
Also, in addition to the ship itself you will find a museum with a "Nelson Gallery" right next to it (it's an independent attraction, so you'll either need a new ticket or use your all-attractions ticket - which you must have with you at all times because the staff will check it at every single attraction).
All in all this is a most exciting and intriguing tourist and historical attraction. Expect to spend 1.5-2 hours on the HMS Victory alone.