Its okay. Good usage of the former Chimp enclosure- plenty of ropes, horizontals etc for climbing. Marwell please note.... But Twycross have always given their Gibbons plenty of swinging/climbing opportunity.
But if they did that the actual climbing area would have to be restricted (to just the centre)to prevent escape. I think this covered area allows them more scope, though not as attractive as the open air concept perhaps.
'Gorgeous exhibit'? Not sure I would go that far...if you saw it in reality you might think otherwise, but most importantly it has been kitted out with the main essentials for Siamang-plenty of swinging/climbing opportunity.