I think it runs true to Theory's usual sizing - this being the first season, they had some difficulties as Olivier apparently worked on the patterns based on French sizing and they did the fitting of the clothes afterwards, based on Theory sizing charts... It's been a bit messed up, as the jackets were all labeled a size 38 French, but were running closer to Rochas production (not runway) size 36.
Pants/jeans run a bit larger, particularly those that come in inch sizing (about one inch larger than from labels such as Acne that run small/true to size). The large pleat trousers are meant to be worn baggy so maybe that also results in rather large waist sizes...?!
Personally, I found the collection had some lovely pieces that, if styled correctly would sit perfectly in your closet, Softgrey. I couldn't be bothered by all those pieces that fall more towards the dreamy wood nymph style he went for at Ricci, but there were also great jackets, shirts and easy pants/dresses with Olivier's hand all over them in terms of the cut and proportion. They have the ease of Ann Demeulemeester's clothes with a healthy dose of Parisian chic, which I liked.