Dutchman Koeman, who has replaced Roberto Martinez, is an experienced coach who did well with the Saints and knows what players he wants to form a successful team. He brought in six new additions over the summer and will be seeking to make an immediate impact in his first year in charge on Merseyside.
The tricky winger excited under Alan Pardew last season and despite the fee, he is in his prime at 27 years of age and will be look to instantly impress the Goodison faithful.
Bolasie could be a key component of Koeman's team and the Toffees were thrilled to fended off interest from Tottenham Hotspur for his services.
Capable of the sublime on his day but his brilliant moments are few and far between for the most part, so hopefully Koeman can instil some consistency .
Williams knows the Premier League having spent five seasons in the top flight with Swansea City, where he served as inspirational skipper, before making the switch to the blue half of the Mersey.
He is an experienced defender whose reading of the game and tough tackling will help shore up the defence. Having received £50m from Manchester City for John Stones, Everton have moved swiftly to find a replacement and Wales captain Williams is the sort of player to add steel to the back four.
Alongside Phil Jagielka, the Toffees have two players who will help mould the likes of Mason Holgate, Tyias Browning and loanees Brendan Galloway and Luke Garbutt into the first team in the coming years.
Idrissa Gane Gueye - from Aston Villa £7m
Game Gueye was one of a very few players to stand out for Aston Villa last season in their disastrous relegation campaign.
The energetic, combative midfielder is a snip at £7m and is similar to Victor Wanyama who played under Koeman at Southampton. He made 35 appearance in the Premier League in 2015/16 and has already played three times for Everton this campaign.
Expect him to be an ever-present in his role in front of the back four alongside Gareth Barry.
Valencia is a clever signing who could prove to be a good foil for Romelu Lukaku. Valencia has pace and if Koeman plays 4-4-2, he will link up well with the Belgium who has the strength to fend off defenders and feed his strike partner. Valencia scored four goals in 19 appearances in the Premier League last season, but after an injury interrupted run in East London, may get more game time in 2015/16, either as a back-up for Lukaku or alongside their main man.
This is the second time Ronald Koeman has signed his fellow Dutchman. After the departure of long-term servant Tim Howard, Stekelenburg has been signed to go toe-to-toe with Joel Robles and has thus far won the battle by starting all three Premier League matches so far.
Koeman has completed some exciting signings to get the Everton fans excited again. Despite the loss of Stones, the Toffees have recouped that money and used it to buy proven Premier League quality in Williams and Bolasie. The latter is an exciting addition whilst Gana Gueye and Stekelenburg are also clever deals brought in relatively cheaply.
The query remains on Valencia, whose scoring record in England is poor, but if fully fit and given the chance to shine in a new environment, could prove handy .
Tribal's Transfer Rating: 7.5/10