The Hammers started well then got a bit complacent and stopped doing the basics – working hard for each other, allied with good organisation – that helped them do so well last season.
If you compare their focus, discipline and the intensity of their play then, to what we have seen from them so far in 2016-17, then it is no wonder their performances and results have dropped off.
Their only league win so far came against Bournemouth, when they kind of fell over the line with a late winner against 10 men. Against most other Premier League teams they would not have got away with it, but fortunately for them they were up against another team who looked a little bit undercooked early in the season.
In every area of attack and defence, West Ham are less effective so far than they were last season, when they finished seventh.
It is very early days but Bilic has a lot of work to do to get them back to that level, and he has to do it quickly.
Looking at the fixture list, West Ham have got a run of games next where you would expect them to pick up some points, especially at home.
Things have to improve soon because the last thing they need in their first season at their new ground is a situation where they are stuck near the bottom of the table.
The longer this bad start continues, the more it will play on the minds of the players and the fans that their first season after leaving Upton Park is going to be spent battling relegation, rather than pushing for the top six again.
‘New stadium brings added pressure’
I don’t think the West Ham team is lacking ability-wise, or in terms of physical fitness. It is mentally where they just do not seem to be at it so far.
Part of that can be put down to the stadium move. London Stadium is a fantastic arena and a great platform for the players to express themselves, but it also brings added pressure.
Last season, Upton Park was a fortress where the Hammers went 16 games unbeaten between August and April.
It would have been hard enough to repeat that even without having to adjust to life at a new stadium, and it is understandable that they have not taken that form with them.
The trouble in the stands with standing, segregation and stewarding has hardly helped because I know a fair few fans did not want to move anyway, and they are even more unhappy now.
When I played for West Ham, we knew the Upton Park crowd would always try to lift us when we needed them.
But, for various reasons, the atmosphere at London Stadium is very different at the moment, and that needs to change.
Does Payet have a hangover from Euro 2016?
On top of having to deal with their changed surroundings, the Hammers have also been without their superstar – Dimitri Payet – for most of the new season.
Payet had only played 23 minutes out of a possible 630 in all competitions before making his first start of the campaign against the Hornets.
Earlier in the summer there were rumours he was injured and, until the transfer window closed, there was a bit of uncertainty about whether he was staying or not. None of that helped matters.
It feels like everyone was waiting for him to come back into the team because, when he did, everything would be OK.
Despite his brilliant rabona assist at the weekend, obviously things did not work out that way.
Along with Hammers defenders James Collins (with Wales) and Angelo Ogbonna (with Italy), Payet was involved in the latter stages of Euro 2016, which I think is another factor here.
Because of the emotion and adulation surrounding the France team that he was a part of, it would not surprise me if the summer is still affecting him in some way.
If so, I could understand it because I had a similar situation when I was at West Ham and went to the 2002 World Cup with England.
I look back and think physically I was all right – I had not lost a lot of fitness because I was even cycling to keep ticking over when I went on holiday to the south of France after getting back from Japan and South Korea.
But mentally I was not ready and, when I came back, it took me two or three months to really find my feet again.
What happened to the Hammers that season should be a warning too – we started really badly, winning only one of our first eight games, and ended up being relegated with 42 points.
‘Hammers need their team spirit and work ethic back’
A police presence and properly trained stewards who understand a football crowd will make a big difference, and improving the lines of communication between the supporters and the board would help a lot too.
Some fans will still be unhappy, of course, because they did not want to leave Upton Park, but I do think the move is a positive one. The new stadium is fabulous and they are very fortunate to get it. It has brought something extra to the Premier League already.
On the pitch, I am confident Bilic can get his group of players back together again, in terms of their team spirit and work ethic.
They need to keep creating chances the way they did against Watford but, as a team, they need to defend much better. I am not just picking on the defence and goalkeeper there because that has to start from the front with the centre-forward.
Last season they made it difficult for the opposition to break them down and did not concede many goals but if everyone does not dig in and work hard then it becomes very difficult.
Too many players seem distracted at the moment, when they really need to be focused on the new task in front of them.
It is easy when you are playing football with freedom, like this team did when things were going well last year, but at the moment things are harder because they are in a battle and they do not appear to be ready for it.
Trevor Sinclair was speaking to BBC Sport’s Chris Bevan.