Windows 10 is a potentially great upgrade – that’s not quite great yet.

The new Microsoft operating system is an essential redesign. That alone makes it worth the upgrade, as I wrote last week. This week, however, I’m offering a reality check.

After a week of constant use, I’ve found it to be buggy compared to Windows 8.1. While not surprising for a new operating system, the point is that some less-adventurous consumers may want to wait to upgrade.

Related: Windows 10 review: The two-minute version

Windows 10 users have been documenting their challenges with the new Microsoft OS using the hashtag #Windows10Fail.

I won’t go into the entire litany of problems (some of them are minor) but below are the standouts. Note that Microsoft issued a big “cumulative” update for Windows 10 on Wednesday to address a variety of issues. That update may, or may not, address some of the issues below. Time will tell.

The Start Menu: Occasionally buggy

The return of the Start Menu is the single most important change for many consumers. But it’s not quite stable yet. About once a day it’s not accessible for me. It either crashes outright or is very slow to respond.

Edge Browser: Needs work

The new Edge browser is fast -- when it's firing on all cylinders. But at times it stops responding. And at other times has trouble running some websites. (Gmail, for example, doesn't always behave itself on Edge). Again, not surprising for a spanking-new browser. There is an option to revert to Explorer, which may solve some issues: click on the three dots in the upper right-hand corner of Edge and select “Open with Internet Explorer.” My guess is that Edge will improve rapidly in the coming weeks and months as Microsoft issues updates. Let me add that I noted last week that Windows 10 felt faster (snappier) overall compared to Windows 8.1. A lot of that had to do with the fact that I switched to Edge. The problem is -- that snappiness did not persist because of the reasons cited above.

Applications don’t carry over

There’s a reason many businesses wait years to upgrade. Proprietary business applications don’t always work on a new Windows operating system. I’m using a new HP business laptop with a suite of security and business applications. Some of those applications behave differently under Windows 10. In at least one case, a security application caused a time-consuming (read: hours) snafu for me.

Windows 10 freezes

This is a hard one to call because it’s never clear if it’s Microsoft’s fault, the PC maker’s fault, a third-party software provider's fault – or all of the above. I’ve found that general freeze-ups on Windows 10 are more common compared to Windows 8.1. A typical example is when I leave the PC idle for an hour or two and come back: sometimes I’m forced to restart Windows 10 because it’s unresponsive. The root cause can be Windows device drivers (software that controls a hardware component) or bugs lurking in Microsoft code. But, again, it’s never easy to assign blame in these cases.

Firefox doesn’t like Windows 10

The Firefox browser does not perform as well on Windows 10. And Mozilla, the organization that develops Firefox, isn’t pleased. CEO Chris Beard has written an open letter to Microsoft.

Cortana is a work in progress

Cortana is a sophisticated digital personal assistant that understands spoken commands. Because voice recognition is difficult even under the best of conditions, it’s not surprising that Cortana is hit-or-miss. I’ll be charitable and say don’t expect too much from Cortana. Simple commands usually work but tasks like creating and composing (dictating) emails is more problematic.

Finally, note that the stability of Windows 10 can vary dramatically depending on the PC brand and age of the PC. In my case, I’m using a new PC designed for Windows 10 so my experience doesn’t necessarily apply to everyone.

Related: Stop Windows 10 spying dead in its tracks with one free app

I asked Microsoft to respond to some of the “bugginess.” Here's what a Microsoft spokesperson said: “While the vast majority of our customers will be able to seamlessly upgrade, some app or device incompatibilities may exist and will decrease over time. If for some reason you run into an issue, Answer Desk offers one-on-one support from Microsoft.”