Alright, let's look at it a few ways...
The optimistic take:
Derrick Rose is the best PG the Knicks have had since Stephon Marbury minimum even if he's depleted. Going from Jose to Rose is a huge shift. The biggest positive impact here is that Rose and KP running pick and rolls will be one of the most dangerous combos ever and that's before you even take into account that the best wing defender on every team will be on Melo. You're talking about one of the premier slashing PG's in the league with a stretch PF/C and one of the yearly league leaders in gravity rankings (those measure how close defenders stay to a player when he's not holding the ball). The pieces going out aren't star players. Grant still has a lot of development to do and RoLo is a glue guy. RoLo is the piece you complete the puzzle with, not the piece you build around. The big thing is that the Knicks didn't send out a pick to fill the biggest hole on the roster. That separates this from historic Knicks trades.
But the real reason for excitement comes with the cap implications. RoLo, Grant and Calderon are outgoing in this deal and their combined salaries are actually more expensive than Rose and Holiday by around half a million dollars. So the Knicks have added a former MVP who will be motivated in a contract year and they actually gained a bit of cap space. That's just this season though, next offseason is where things get really exciting. Rose is a 21 million dollar expiring player and Rolo/Grant were both on the books for a few more years. Couple the added cap room with the cap increase next offseason and the Knicks stand to have a ton of room for a much stronger FA class in 2017 should they choose to be conservative in this offseason. It also adds a third marquee name to sell top FA's on in negotiations this offseason. So the acquisition itself might be an afterthought.
The cynical take:
Derrick Rose can't stay healthy and had chemistry problems next to another star in Jimmy Butler. This is another ball dominant player next to Carmelo while KP is in danger of losing touches that would help his development. KP could easily see himself become a third option now rather than a second option developing his way into the first option. On top of that, what good is bringing in a decent PG when he can't stay healthy. The Knicks still need to invest in a STRONG back-up PG because there's virtually no way that Rose will play a full season. To add insult to injury, the Knicks just traded away a potential future starting PG on a rookie contract along with a true two-way Center who was on one of the best value contracts any big man has. Watch the prices of Centers in this coming offseason, RoLo's value will be higher just off of the comparison to other starting Centers' contracts.
But what makes that even uglier is that Rose is a rental player. This is a guy who apparently wants to be a max player again, that could interfere with him playing team ball. He had rumored locker room issues with Jimmy Butler, so who knows how he'll deal with another alpha in Melo. Ego is a scary thing and can ruin a locker room. On top of that, this band-aid at PG created an equally scary gaping wound at C. KP might be an answer there but that still leaves a hole at PF. Either way, this filled one starting spot by making a hole at another starting spot...and there's virtually no chance we replace RoLo for the same price or cheaper. I doubt even a Bismack Biyombo will be cheaper than 12.5 per year. So any cap space in next offseason likely gets cut into deeply by our needs at SG and PF/C. Add the holes along the bench and this team had too many needs to move two value contracts for a one year deal.
My Final Thoughts:
It's honestly somewhere in between the two takes, just like with anything. The trade itself is something I don't like. Grant and RoLo stood to be around with KP for a while and Rose has a strong chance to be a one year rental...I'm not sure I want someone so injury prone to be around longer even if he does play well. The reality is that this isn't a move that can be looked at on it's own. It completely changes our needs for this offseason. This FA class has better bigs than PG options and with Melo able to play both forward spots and KP able to rock PF or C, there's even more flexibility to build with. The hope here is that Phil has some tricks up his sleeve. He mentioned in March that Agents were already blowing him up, hopefully he had a serious plan. Right now, I don't like this move, but given that it left us with all our cap room...I'm still gonna hold my breath and hope that Phil will follow up with moves that are meaningful for the long term roster.
Edit: I should have added that I actually like Justin Holiday. He has 3-D potential as a wing and he's got athleticism. As a back-up guy and developmental piece, he's at least worth a look and could even show some upside.