Adding to previous suggestions:

The slots game is boring because the maximum multiplier currently is 5x, or a £500,000 at max bet.

Adding the possibility of one or two really big wins would make it much more exciting.

The easiest way to do it would be to scale up the existing pay table and reducing win frequency. For example, the highest fruit could be 100x and wilds be 1000x.

Higher bet options would be nice too, although I won't be using them yet :)