While the Ryan trade looks bad now it was a pretty decent move for them at the time (even though IMO Ryan was already declining at the time of the trade), they were getting a consistent 30 goal forward in his mid 20's coming off 1 bad season. And gave up Silf (who was a very good young 2 way forward, but questions if his offense could get to that next level in the NHL), Noesen (young prospect coming off an underwhelming +2 season) and a 1st rounder (which was expected to be around the 20's) - honestly that's the sort of move you want your team to take if they are looking to compete, it didn't work out well but if Anaheim was in the same situation where they thought they had a window to compete, I'd rather see them take a shot and go for it then be overly conservative (which you could certainly argue Anaheim may have been overly conservative in their window to date).
Phaneuf trade was a good one for Ottawa tbh, they got rid of a ton of deadwood who were signed for multiple years (Michalek, Cowen, Greening) which made room for them to re-sign their best forward in Hoffman. Granted Phaneuf contract is brutal longer term, he's at least a serviceable middle pairing guy and they have Hoffman signed up for a couple more seasons at a pretty great AAV.
I think it's to early to say the Duchene trade is terrible for them. On paper Duchene has been the more productive player since 11-12 (so when Turris joined the Sens), not to mention the Sens hands were a bit tied as Turris was obviously not going to re-sign in Ottawa which affects the value of Turris in a trade somewhat. So to turn a UFA to be into a similar player (at worst), who's signed through 2019 and only having to give up a very good prospect (who theoretically isn't needed if they see Duchene as a #1 center) and a 1st and 3rd rounder isn't the worst trade. Ottawa at the time were 5th in the Eastern Conference overall with a record of 6-3-5 so giving up a 1st rounder for 2018 was hardly a disaster as they were playing pretty decent hockey. I don't think anyone could have predicted Duchene would struggle to adapt so badly and for Ottawa to end up going 5-11-3 since the trade. Assuming Duchene picks it up and Ottawa is able to re-sign him past his current deal, I think it still ends up a pretty good deal for Ottawa.
The only real headscracther is the Brassard/Zibanejad trade, but I have a feeling it was a financial move more then anything (because honestly nothing else makes sense). The owner is a noted cheapass and would probably rather only have a 3 year/15m commitment to Brassard compared to a 5 year/27m commitment to Zibanjad.
Honestly I think Ottawa get more flack for their moves then they deserve. It's easy to look back in hindsight and say they are terrible, but outside of the Zibanejad move all of their recent big moves made sense at the time, granted the Ryan one turned out terrible in hindsight.