First, there is no simple way to get cannabis. You cannot just go into any shop, only a select few cities or regions will be allowed to have shops, and that is only for a limited "evaluation period". I predict that after this evaluation period, there just won't be anymore shops. You could participate in a cannabis growing club that is intended as a communal kind of homegrowing, but there are very strange regulations around that such as "at least 200m from any school/kindergarten". Because maybe kids only sneak into greenhouses that are within 200m of their school? Which leaves homegrowing, but the security requirements for the fentanyl in my medicine cabinet are less than for my future potted plants. So they decriminalized cannabis but gave the police reason to snoop around in homes and just fine the same people for different "crimes", such as insufficiently armored windows in front of their indoor garden.
Then, the law will conflict with EU laws. But the government didn't even try to change EU laws, they are just waiting to maybe be sued by the commission. Which will then end in the law being invalidated by the EU courts.
They also added taxation, with the argument that this will generate income to offset the supposed health problems that legalization would create. However, since the only viable thing is to homegrow, which isn't taxed (yet), tax income will be minimal and just add to the overall tax bureaucracy, maybe even resulting in a net negative income for the state.
There were ideas of creating a cannabis industry, similar to what California did. However, since there won't be many shops, requirements around security are extreme and customers are driven to homegrow, there won't be any industry to speak of. Maybe just a little to illegally (because trade is forbidden there, as is exporting from Germany) supply the Netherlands and other neighboring countries. Since there won't be any scale and costs will be high, illegal cannabis will still be cheaper overall.
I personally suspect that this law is set up to fail by the people writing it. E.g. the minister of health, Lauterbach, was never a fan of the idea (to say it mildly), yet was forced to write this law since it fell into the realm of his ministry. Others in the coalition, especially in the SPD, are of a similar opinion and only go along because their other partners, FDP and greens, demanded legalization. When the next government in 2 years is a SPD/CDU coalition (current polls look that way, would be a repeat of most of the Merkel governments), this law will, after "thorough evaluation of the results", be abolished again.