The Pear Tree is good, but can be a bit pricey (imho). You could try the Vale of the White Horse Inn, in Minety (max 15 mins from M4 junct16) or the Sally Pussey on the road to Wootton Basset from junct16 (2 mins). If you google these you should be able to get directions. If you like Asian food, 'Cosmo' in Town is quite an experience, but always busy, so book ahead.
Depending on your interests, there is the Steam Museum in Swindon, right next door to the Designer Outlet shopping centre (shame!). Also, the Swindon and Cricklade Railway (Steam & Diesel) is about 10-15 mins from your hotel (do you see a theme emerging?!).
Alternatively, Avebury isn't too far away, or you could go walking on the Ridgeway & visit Barbury Castle.
Lydiard Park is nice for a short walk, and there's a house & gardens to visit (don't know about entry charges, sorry); it's about 5 mins from your hotel. Also there's a bigger country park 'Coate Water' on the opposite side of town. If you look on the Swindon Borough Council website you should find more info about these places.
That's about all I can think of right now; will ask DH what he thinks tomorrow. The actual centre of Swindon isn't that exciting - the same shops etc that you find on most high streets these days, and not many independent ones.
OTOH, Wootton Basset is a lovely little market town with some nice shops (OK, nothing earth shattering, but we like it!), and is only 10-15 mins drive from your hotel.
Hope you have a good weekend, whatever you get up to!
Jo x