I will just post a few thought about my trip
Day 1 - Planckendael
Rain in the morning and grey but dry weather during the day. Perfect weather for a zoo-trip as it kept most of the crowds away (plus it was Monday) and gave me lots of peace and quiet to enjoy the large open-range zoo outside Mechelen. It was a bit nippy in the weather so a few species kept mostly to their indoor exhibits (bonobos, golden-headed lion tamarin, white-faced tamarins, etc.) but most animals were out and about and the before mentioned species could also be seen indoors.
I had visited Planckendael in 2006 but it was even better that I remembered. My "old favourites" were the Bonobo exhibit, the Oceania exhibit, the European exhibits and the Asia theme. When I visited in 2006 the Asian Tropical House was brand new and hardly vegetated at all. It looked MUCH better this time with dense vegetation and active birds. The giraffe and cheetah exhibits were new for me and both really well done. Nothing extraordinary but well executed. I was also very impressed with the signage throughout the park which was generally really good (and in three languages even).
Through a combination of luck and perseverance I managed to see all of the "difficult" species and that I really wanted to see that day and saw some very active Eurasian badgers, common wombats and short-beaked echidnas.
Day 2 - Pairi Daiza
Went to the formerly known Parc Paradisio on the second day and found it far out into the countryside with no real difficulties. Had pretty good weather the first half of the day but rain for the last few hours. I was very impressed with their bird collection and the "old" part of the zoo. The Oasis Tropical House and adjoining aviaries and birdhouses were a positive experience even though I am not bird expert.
Positives in the park included the Mersus Emergo ship with the terraria and very nice exhibitions about conservation as well as the outdoor elephant, hippo and siamang enclosures. Also the walk-through exhibit for squirrel monkeys and the huge aviaries for birds of prey were a joy to see. However, the place I enjoyed most were in fact the huge Chinese Garden with many species of crane and stork as well as red pandas, Chinese muntjac and kiangs.
Unfortunately for me a large part of the park was closed for construction during my visit. The whole Nosy Komba island (lemurs), the shoebill aviary and savannah were all levelled to the ground. Does anybody know what they are building there?
I was actually a bit disappointed about the newer developments in the park. Both the Australia and Kingdom of Ganesh exhibits seemed to have lots of many pumped into very little. The Australia exhibit was very large but had quite few exhibits in it compared to the size. The Kingdom of Ganesh was even worse. It has huge slaps of mock rock shaped to the biggest fake temple ruin I have ever seen. While it was impressive I feel that the money could have been spent better. The only exhibits there were a pretty good exhibit for crested black macaques and mediocre to substandard exhibits for water buffalo, Indian porcupines, small-clawed otters, armadillos (?) and meerkats (???).
All in all Pairi Daiza as a positive experience but not as good as I had hoped. I will probably visit sometime again but it is unlikely that I will go out of my way to do so.
Day 3 and 5 - Antwerpen Zoo
Fine weather and very few people in Antwerpen Zoo on day three. Antwerpen Zoo was even better that I remembered. As in Planckendael the zoo had some of the best signage I have ever seen (again in three languages). New exhibits for me included the extension areas with exhibits for okapis, dik-diks, babirusas and wallabies as well the the breeding centre for Congo peafowl. Unfortunately, the new lion exhibit wasn't quite ready yet but it was complete enough for me to get and idea of how it will be with lions, meerkats and mongooses in there. I was completely fascinated by the two eastern gorillas where I could have stayed for hours (which I almost did). I spent to days in Antwerpen Zoo so I had plenty of time to see the whole zoo several times. Enjoyable exhibit were the ones for spectacled bears/coatis, okapis, Congo peafowl, Hippotopia, Vriesland (unfortunately without otters now) and the outdoor exhibit for Asian elephants (a bit small but well designed). Antwerpen Zoo is a beautiful old city zoo and highly recommendable.
Day 4 - Museums
Spent the day visiting a few museums in Brussels. Went first to the Natural History Museum and then the Military History Museum. Both were enjoyable but not something I would recommend unless someone has a REALLY specific interest. Regretted that I had not gone to Blanckenberge instead.
Day 5 - Aquatopia
On my last day I went to Antwerpen again this time starting out in Aquatopia located right next to the zoo. I had not expected much but was pleasantly surprised. I only spent 1,5 hours at the aquarium but that was enough (unless you are really interested in fish). Aquatopia had a very Sea Life-ish quality too it (unfortunately) but some nice tanks with Mangrove species as well as the shark tank with black-tipped reef, nurse and zebra sharks. After Aquatopia I could check zoo nr. 103 of on my list

After Aquatopia I hurried over the Antwerpen Zoo and stayed there for the rest of the day as well as ended up giving lectures on gorillas for English tourists.
All in all a pretty good trip!