The French forward came back with a bang after struggling against Manchester City, with the colossus scoring twice on Saturday at Vicarage Road in a 3-1 victory over Watford.
Haller arrived at the London Stadium from Eintracht Frankfurt in the summer, with the 25-year-old being deployed as a lone striker so far with other signing Albian Ajeti being named on the bench as a potential back-up.
West Ham were reported by the Evening Standard to have paid £45million to the German club, a club-record fee the year after breaking their record twice in one summer.
The Evening Standard then reported after the Watford game, that Haller could eventually end up costing £55million, which is £10million more than the first-suggested fee.
Either way, the forward will be worth every single penny on the early evidence – with the 25-year-old showing he has what it takes to succeed in the Premier League.
Last season, Haller was involved in 24 goals in Germany, scoring 15 and assisting a further nine – as he won an average of 6.9 aerial duels per game, according to WhoScored.
Should the Frenchman replicate that sort of form then Manuel Pellegrini will no doubt be delighted, and his ever-changing transfer fee will be background noise.
So far, Haller has started well, scoring his first two goals for the club. More impressively, he has continued to dominate in the air, winning an average of 4.5 aerial duels per game, as well as averaging 2.5 shots each outing [WhoScored].
If those sort of stats continue, Haller could easily score more than the 15 goals he delivered last season, with the Hammers relying on him more for his goals rather than his assists.
At Frankfurt, Haller was alongside Luka Jovic and was selected to create chances as well as score them. At the Hammers, with players in midfield such as Felipe Anderson, Manuel Lanzini, and Pablo Fornals, he can fully concentrate on scoring the goals himself.
Even if they do need to pay up to £55million, the 25-year-old will be worth every single penny if his early-season form is anything to go by.