I have had the watch for 1 month. On the positive side, the measurements are very good, nothing like the smartwatch I had before. The screen is very clear under the sun, although it is not AMOLED. The smart functions of the watch are very good for me, and the touchscreen has good responsiveness. It is comfortable to wear and very lightweight. The Garmin applications are very good.

On the negative side, the screen is not AMOLED (hence one less star) like the VENUE, and for the price, it should have better resolution. (I chose this watch instead of the VENUE solely because of the battery, which lasts longer and doesn't require daily charging.) The battery lasts me 3-5 days (depending on the watch face) without having everything open, compared to my previous Huawei watch where I would forget what charging even meant. The durability as a material did not impress me because it left a small mark on the bezel with the first impact (again, compared to the Huawei where nothing happened).

Overall, I am satisfied because I knew what I was looking for: a more accurate watch for sports measurements, with some smart functions that help in daily life, but lacking in screen resolution compared to watches with AMOLED and a slightly lower battery, which is still satisfactory considering other comparable watches that require daily charging.

I got it after a big dilemma and research (I was torn between this and the venu).
I ended up choosing this for the following reasons: better battery life (the venu's amoled display only lasts half as long). Additionally, the venu has a smaller case and an 18mm strap, making it look almost like a women's or unisex watch (although some people may like that). The vivoactive also shows the home screen even when it's off (always on display) without backlight, which unfortunately doesn't happen with the venu and helps save battery (meaning you have to tap the screen to see what's happening on the venu). So, if someone isn't interested in flashy colors and the resolution of the amoled, which is beautiful, then the vivoactive 4 is the way to go since they have the same functions.
Other than that, the watch has incredible quality and feels great on the wrist. The battery lasts a long time and the measurements are very accurate (floors, heart rate, steps, etc., heart rate compared to indications on a professional treadmill and a blood pressure monitor). The Garmin app takes everything to the next level, I really don't think there's a better application for a sports watch. There's a plethora of watch faces available on the Connect IQ store app, where you can find anything you can imagine. Choose the "SkyTracker" watch face if you want, it's beautiful and has all the information on your home screen without being tiring or confusing.

Update 21/10/2020: After 4 months of use, battery life depends largely on the watchface you use (apart from active functions). Duration with a custom "heavy" watchface is approximately 3 days. It also depends on the format of the watchface (screen color, functions, etc.). Duration with default or custom watchface that you create is 5+ days.

I made this particular purchase after extensive research for a beautiful, durable, and reliable sports watch at a relatively reasonable price that can be worn comfortably on a daily basis with basic/useful smartwatch functions. In addition to dozens of reviews and review videos, I spoke with owners of various smartwatches, both athletes and non-athletes. The conclusion was the same: try Garmin. I have had it for about 3 weeks now and it has pleasantly surprised me. It does exactly what it says, with a commendable battery life, which is the big advantage for me compared to popular smartwatch brands that may play YouTube videos but only last a maximum of one day. Of course, battery life is affected by the functions you choose to run simultaneously. I recommend purchasing it with screen protection (around €7), as the screen is exposed due to its size and architecture. The instant synchronization with the mobile phone and flawless call reception/answering through headphones is incredible. Messages or emails also appear in full, unlike competitors. You can reply with many predefined answers that you set through the application. The connection and playback of music with airpods is stable and without issues, except for the (one) first time that required reconnection. An important advantage is the flawless touchscreen operation - a rare feature for Garmin - which facilitates use and was one of the selection criteria compared to other models of the same brand (those who want an OLED screen, etc., should go directly to Venu instead of Vivoactive). The GPS connection is impeccable and fast, as long as the criterion set by Garmin is met from the beginning: outdoor use without obstacles above you (e.g. overhead power cables). It also supports Wi-Fi. The offerings in running training programs (which concern me) and statistics are on another level compared to apps like NRC. Perhaps it is not a watch for a casual athlete who runs, for example, once a week. The measurements appear accurate, except for the sleep function, which, as far as I understand, only measures the pre-set sleep period as sleep time.

Countless watchfaces and generally many applications are available through the Garmin store. The application on the mobile phone is somewhat slow and the desktop application definitely needs improvement in the way music is imported from the computer. The use of the buttons/functions of the watch is a matter of habit.

In conclusion:
The Vivoactive 4 is a watch for athletes that can be worn on a daily basis as it is beautiful (people ask me which watch it is) and functions perfectly with basic smartwatch features such as receiving notifications, answering calls (with headphones), playing music without the need for a mobile phone (incredibly useful for running), making transactions with the watch (for Greece, Revolut and Alpha), and all of this with a relatively long battery life.

I have been the owner of the vicoactive 4 for a month now!
The watch is lightweight, you almost don't feel like you're wearing it, very accurate measurements (only a slight inaccuracy in sleep tracking), satisfactory battery life I would say! Very responsive touchscreen! It has several preloaded sports profiles that personally cover my needs! The body battery and stress level tracking are very good, so you know when your body is ready for the next activity! In my opinion, the watch is amazing overall and worth it!

update 6/23/20 After 4 months of use, the watch has not had any issues at all! It works like the first day and constantly receives software updates from Garmin! I am very satisfied!

update 4/3/2022 almost after 2 years of continuous use, the watch works perfectly! The only negative (if we can call it negative) is a slight battery degradation, which I consider normal! It continues to receive software updates from Garmin normally! In conclusion, it is worth its money and even more so at the current price!