There is already concern - even admitted by UEFA - that this may lead to collusion among two competing teams in a group, who could try to engineer a result to ensure they both finish higher than a team in another group.
It will also make qualifying mostly irrelevant and devoid of intrigue as all the top tier nations will be virtually guaranteed a passage to the final tournament.
Finally, the expansion will preclude smaller nations from hosting the tournament, as they won't have the infrastructure and stadiums to handle 24 teams and 52 games, meaning that hosting rights will be rotated between a few select nations. UEFA is currently struggling to find a host of their 2020 tournament; a Scandinavian bid has not materialised, Germany has apparently backed out and a proposed joint venture between Azerbaijan and Georgia has also not come to fruition, leaving Turkey as the only current bid.
The impetus for change was initially brought about by the Republic of Ireland and Scotland, who argued that the breakup of some European states (especially in the Balkans and Eastern Europe) justified the increase. But since the last expansion in 1996 (from eight to 16 teams) the number of UEFA member nations has only increased from 48 to 53 and the European confederation includes tiny states like Andorra, Liechtenstein, Luxembourg, Moldova and the Faroe Islands. However, the main driver of course is money. UEFA will bank $2.1 billion this time round but that will only rise with more teams and games. They may come to regret their abandoning of the 'sweet 16'.