Slot, ahead of Sunday's clash at Burnley, discussed signing the former Newcastle United striker on deadline day.
He said of the £125m deal: "A lot happened on the last day, which isn't always the situation but the thing that pleased me most is us getting Alex over the line.
"Everyone worked so hard to get the deal done. It's good for the club, fans, players, me - all the work they put in resulted in Alex signing for us."
Slot admits he was pleased with the way Sweden coach Jon Dahl Tomasson managed Isak's minutes during international week.
Praise for Tomasson
He said: "Fitness-wise? First of all, the Swedish manager Tomasson deserves a big compliment because he gets maybe the best striker in the world in and needs him for his country but understands thst playing him might result in injuries, so he took care of the player and he deserves a big compliment for that.
"We will treat Alex the same, so don't expect 90 minutes every week, he missed pre-season and team sessions so we have to build him up graudually. But that will be a challenge but we have signed him for six years, so this is what the fans have to keep in mind if I bring him in."
On the anger of Newcastle fans aimed towards their former centre-forward, Slot added: "In football, there's always criticism, sometimes they cheer for us; after the League Cup they were happy with him, in other moments you get criticised, this is part of his life, my life and now he is a player for us."
Asked about how Isak has settled over the past week, Slot admits he's had little to do with his new signing.
"Maybe don't believe me but I haven't spoken to him that much. I phoned him after he signed and he had to go to Sweden but 99 percent of the time during breaks, I leave the players for their national managers.
"I texted him once or twice but I do have to get to know him in the upcoming days and weeks. But we have such a great culture here at this club, so we sign players for his qualities and I know how good he is, what a quality player he is.
Tribute to Elliott
Slot also discussed their late market departures, with Luis Diaz leaving for Bayern Munich, Harvey Elliott for Aston Villa and Tyler Morton for Lyon.
Slot says management is proud of how all three players have kicked off the season at their new clubs.
He said, "Not only Harvey but Luis Diaz hit the ground running at Bayern Munich, Tyler Morton too at Lyon, so that tells you how we bring players to other clubs. It's in the interest of Harvey and everyone, he didn't get the playing time he deserved but he was always doing what was in the best interests of the club, he deserves the compliments for that.
"Players like him were definitely the reason we could win the league, he was always positive and that is part of the success of the team, players who don't play much have the right mindset."
Upset Chiesa?
The Dutchman was asked about leaving Fede Chiesa out of their Champions League squad for the group phase. Despite his decisive form, Chiesa was not registered by Slot.
He explained, "Of course it was tough for a manager, it is difficult for him. Of course he wasn't happy with that decision but he understood the argument.
"He gave the answer you want to hear from a player and he will be there to help in the other cups and the league. He worked really hard in these days to be ready for the upcoming games, which is even more important than what a player tells you."
Burnley a good team
On going to Turf Moor this weekend, Slot says there'll be no underestimating the Clarets.
"Defensively solid, but they have so much more. Their goal against Sunderland was a very good team goal," said Slot.
"So, a good team. Look, I know how strong these teams can be. Last season, we had problems at Ipswich, we had problems at Leicester and we had problems at Southampton.
"We know every game is difficult and I only have to look back at last season to understand that."
Guehi was close
Before signing off, Slot also expanded on Liverpool missing out on signing Crystal Palace defender Marc Guehi on deadline day.
The two clubs had agreed a £35m fee for the Palace skipper, but the deal was blocked in the final minutes by the Eagles after their manager Oliver Glasner threatened to quit over the sale.
Slot said: "I think it would be ridiculous if I will deny we were close, it was so out in the open, these things happen in football. It's happened to our players before, it can happen. We would like to sign him of course because we were in for him. If we feel we can strengthen then we try to.
"It's a pity for the player but he is at a good club. Let's see what the future brings for us. January or summer? I don't tell you but I am thinking of Burnley."